Abstract
AbGradCon 2011 Oral Presentations
Evidence for the Homogeneity of Abiotically Synthesized Organic Matter in the Solar System
Because carbonaceous chondrites (CCs) represent some of the oldest and most primitive materials in the Solar System, their organic matter content can be used to decipher the history of prebiotic organic chemistry and how it may have resulted in the development of life on Earth. Many families of organics have been identified in CCs, among them; monocarboxylic acids (MCAs) are of particular astrobiological importance due to their high abundance, and their potential role on the evolution of the lipid bilayer of the cell membrane. MCAs can be found in their free form or derived from insoluble organic matter (IOM) in CCs using RuO4 oxidation. The content and distribution of free MCAs can be greatly affected by secondary thermal and aqueous alterations on the parent bodies. IOM-derived MCAs, in contrast, may be far more resistant to these secondary alterations. To better understand the impact of secondary alterations on the composition of MCAs and IOM, we determined the distributions and isotopic ratios of free and IOM-derived MCAs in six carbonaceous chondrites with very different secondary alteration processes. We found that free MCAs show dramatically different distributions in different samples, however; IOM-derived MCAs are very similar regardless of the degree of thermal and aqueous alterations. Our data suggest that aliphatic structures are well preserved in IOM despite of the major secondary alterations. The high degree of similarity in IOM-derived MCAs suggest a common origin of abiotic organic matter throughout the Solar System.
Extragalactic Cosmic Rays and Terrestrial Biodiversity Cycles
A ∼ 62 My periodicity in terrestrial biodiversity has been observed in independent studies of paleobiology databases going back to 500 My. The period and phase of this biodiversity cycle correlates with the motion of our solar system in the galactic disk that oscillates perpendicular to the galactic plane with an amplitude of about 70 parsecs and a period of 63.6 My. Our Galaxy is falling toward the Virgo cluster due to its gravitational pull, forming a galactic shock at the north end of our galaxy due to this motion, capable of accelerating particles and exposing our galaxy's northern side to a higher flux of cosmic rays. These high-energy particles strike the Earth's atmosphere initiating an extensive air shower, ionizing the atmosphere by producing charged secondary particles. Increased ionization leads to changes in atmospheric chemistry, resulting in ozone depletion, which increases the flux of solar UVB radiation at the surface and is potentially harmful to living organisms. Secondary particles such as muons produced as a result of nuclear interactions are able to reach the ground, enhancing the biological radiation dose, causing DNA damage and increasing mutation rates, which can have serious biological implications for terrestrial and subterrestrial life. Using a Monte Carlo simulation package CORSIKA, we quantify these effects resulting from enhanced cosmic ray exposure and discuss their impact on the Earth's atmosphere and terrestrial biodiversity.
Chroococcidiopsis atacamensis, a New Hypolithic Cyanobacteria Isolated from the Hyperarid Atacama Desert
The Atacama Desert is the driest place on Earth, with an arid core highly adverse to the development of life. Here, we report that along the coast in these arid regions, complex associations of cyanobacteria, archaea, and heterotrophic bacteria inhabit the undersides of translucent quartz stones. Colonization rates in these areas, which receive virtually no rain but mainly fog, are significantly higher than those reported inland in the hyperarid zone at the same latitude. This finding strongly suggests that hypolithic microbial communities thriving in the seaward face of the Coastal Range can survive with fog as the main regular source of moisture. A model is advanced where the development of the hypolithic communities under quartz stones relies on a positive feedback between fog availability and the higher thermal conductivity of the quartz rocks, which results in lower daytime temperatures at the quartz–soil interface microenvironment. From this site, we were able to culture several species of cyanobacteria, one of which we identified as a new species of the Chroococcidiopis genus, highly tolerant to low water availability. This tolerance seems to be explained, in part, due to the production of high amounts of sucrose that work as an intracellular compatible solute that helps to maintain cell ultrastructure under these stressful conditions.
Acidophilic Iron-Sulfur Bacteria and Their Relevance for Mars
During the last few decades, orbiter and lander missions to Mars have revealed extensive regions of layered deposits, composed of ferric oxides and sulfate minerals. These sediments indicate the possible existence of an aqueous, acidic environment in parts of early Mars. Bacteria similar to chemolithoautotrophs on Earth, known to strive in acidic, iron- and sulfur-rich environments, could have been an integral part of a potential extinct martian ecosystem, and might possibly even exist today in protected subsurface niches. Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans were chosen as model organisms to study the ability of iron-sulfur bacteria to survive or grow under simulated martian subsurface conditions. Different viability markers are used to give a more comprehensive view on bacterial activity and death. Both microbes can utilize a variety of electron donors and acceptors for energy-generating redox reactions, and are facultative anaerobes. They are also able to grow on mixtures of Mars analog regolith, composed of Mars-relevant iron-sulfur-minerals, without additional nutrients. Their resistance to single stress factors such as desiccation, high salt concentrations, low pressure, UV and ionizing radiation, and low temperatures is investigated. Both organisms are sensitive to short-term desiccation, and the presence of minerals does not exhibit any protective effect. However, when grown as a biofilm, the bacteria are able to survive longer periods of drying. Ongoing experiments aim to adapt the bacteria to Mars-like conditions and expose them to combined stressors in a Mars simulation chamber, creating a subsurface environment.
An Evaluation of the Inefficiency Objection in Origin of Life Theories: A Lesson from Simpson's Paradox
The “inefficiency objection” states that the reactions proposed by competing origins of life theories are both too inefficient and not specific enough to explain the generation of early life. We use the Simpson's paradox (SP) as a tool for challenging this objection. We argue that on primitive earth, reactions could be inefficient locally, yet they could be simultaneously efficient as a whole, leading to life's emergence.
SP involves the reversal of the direction of a comparison when data from several individual groups are combined to form a global whole. In molecular dynamic cases of SP, we observe, over a period of time, the reversal of which molecular product evolves to become the major product globally when sub-reactions are pooled together. Take each sub-reaction of the reverse TCA, the functional molecules, citric acid, grow at a slower rate than the non-functional molecules, succinic and glyoxylic acids, an inefficient reaction. With the help of SP, we, however, show that although functional molecules grow less rapidly than the non-functional ones in many sub-reactions, the functional molecules can emerge as the major products globally. This indicates that the production of reduced carbon and functional RNA from prebiotic precursors can be far more chemically plausible globally than indicated by RNA world, or metabolism first theories' detractors. If a reaction can be efficient globally as shown by SP, then the inefficiency objection to the origin of life theories is untenable, thus the emergence of life on early Earth seems more probable than ever before.
Conjecture on the Possibility that the Highly Selective Response of DNA to Ionizing Radiation Was an Evolutionary Force in the Origin of Life?
Life originating around 4 Ga was exposed to high fluxes of ionizing radiation. Ionizing radiation creates damage by two distinct mechanisms: (i) the indirect effect is by energy absorption in the water, creating reactive water radicals that attack biomolecules, and (ii) the direct effect is by energy absorption in the biomolecule itself. In mammalian cells, the direct and indirect effects are approximately of equal importance. This talk will focus on damage produced in nucleic acids by the direct effect. Damage to DNA by the direct effect is surprisingly selective. Ionization creates an electron-loss site (called a radical cation or hole) and an electron-gain site (called a radical anion or reduced site). From pulse radiolysis, EPR spectroscopy, and product analysis, quite a bit is known with regard to the initial distribution of holes and reduced sites and the final products stemming from these initial radicals. One-electron reduction is exclusively at Cyt and Thy, with initial electron capture by Cyt being ∼10 × greater than Thy. Holes are preferentially trapped by Gua, Ade, and deoxyribose, with approximate ratios of 10:1:5, respectively. Therefore, damage is highly selective for CG and exceeds damage to deoxyribose by ∼4 fold. In regards to backbone damage, the ribose of RNA is significantly more susceptible to hydroxyl attack than is the deoxyribose of DNA. Conjecture is given on how the differences between the radiation responses of RNA vs. DNA would drive the evolution of an RNA world into a DNA world.
Constraining the Number of Habitable Planets Using Debris Discs
A decade before the discovery of the first extrasolar planet came the discovery of debris discs. Debris discs are discs of dust and planetesimals similar to the asteroid and Kuiper belts in our own Solar Systems. The properties of these discs can be used to provide us with information about the planetary systems they inhabit. Locations of the dust and structure in the disc can tell us about interactions between the disc and planets both past and present. Information on the disc can also tell us about the level of cometary bombardment any habitable planets may be receiving. It is thought that the inner Solar System went through a period known as the Late Heavy Bombardment (LHB) about 800 Myr after its formation caused by the migration of the giant planets. I present models of the observable properties of the Solar System throughout its history, showing the effect of the LHB on the debris disc, and compare these with the statistics of observed debris discs. I find that events like the LHB are rare, occurring around less than 12% of Sun-like stars. I then show results of simulations of dynamical instabilities, showing the connection between cold debris discs and the presence of habitable planets. I show that our modeling predicts that approximately 60% of Sun-like stars should have terrestrial planets. I conclude by discussing the implications for the number of habitable planets and the fraction of these systems likely to have life.
The Positive Cooperation of a GTPase and an Fe-S Protein: The Interaction of Two Functions Likely Present During Abiogenesis
Hydrogen metabolism, as evidenced by its presence in a wide array of organisms from diverse evolutionary backgrounds, was likely an important process present at the origin of life and a key component to early life. One of the enzymes that reversibly reduces protons to dihydrogen, [FeFe]-hydrogenase, has a complex metallocofactor that consists of an Fe-S cluster with biologically unusual ligands carbon monoxide and cyanide, as well as a dithiolate linker. This complex metal cluster, termed the H-cluster, is biologically synthesized by two Fe-S containing radical S-adenosylmethionine (SAM) enzymes and one Fe-S containing GTPase. The P-loop motif responsible for coordination of nucleotide triphosphates like GTP is believed to be one of the most ancient markers of early biological catalysts. Additionally, non-biological and protobiological Fe-S clusters were likely important in catalyzing small molecule interconversion reactions (such as hydrogen oxidation and reduction reactions) during the transition period from abiotic to biotic processes. We have recently shown a positive interaction exists between the radical SAM enzyme HydE and the Fe-S containing GTPase HydF during H-cluster maturation. HydE and HydG both increase the GTPase activity of HydF by 50%, indicating a role for GTP hydrolysis in forming the H-cluster precursor and providing a link between Fe-S systems and P-loop nucleotide triphosphate systems. Despite the fact that the modern enzymes have undergone extensive evolutionary refinement, the H-cluster biosynthetic pathway provides an excellent experimental model to probe the potential coupling of Fe-S catalysis and GTP binding and hydrolysis for the processes associated with a burgeoning biotic world.
Do the Elements Support a Hydrothermal Origin of Life?
A number of genomic and proteomic features of life on Earth, like the 16S ribosomal RNA gene, have been recognised as being conserved over billions of years. Genetic and proteomic conservation translates to conservation of metabolic pathways to varying degrees across taxa. It follows that the stoichiometry of elements that make up the cellular components will be conserved to varying degrees across taxa.
Based on the similarities in the elemental composition of Eukarya (as represented by humans) and Bacteria, we suggest that the stoichiometry of life, i.e. its bulk elemental composition, is a conserved feature of life on Earth. This allows us to infer the elemental composition of the Last Universal Common Ancestor (LUCA). Since, the elemental composition of an organism will also reflect to some extent the elemental abundances in its environment; we suggest that the inferred stoichiometry of LUCA could be used as a proxy for the stoichiometry of its environment.
I will present elemental abundances in the fluids around different types of hydrothermal vents and compare it to the inferred abundances in LUCA. The results could enable us to exclude certain hypothesised sites for the origin of life such as surface ocean waters but also help us identify modern analogues of geological sites such as hydrothermal vents where LUCA may have existed and where life first evolved from its prebiotic origins.
Reactions of H Atoms with Anionic Carbon-Nitrogen Species in the Gas Phase
A fundamental goal of astrobiology is to discover the origin of life in the universe. An intimate knowledge of the chemical reactions taking place in the interstellar medium (ISM) may contribute more pieces to this complex puzzle. Reactions involving organic molecules are especially important to astrobiology. Several carbon- and nitrogen-containing anions have been spectroscopically detected in the ISM, and this study focuses on their gas phase reactivity with the most abundant interstellar species, hydrogen atom. The tandem flowing afterglow-selected ion flow tube (FA-SIFT) was used to experimentally determine the rate constants, products, and branching ratios of these reactions. CnN− (n = 1-6),
Models of Martian Hydrothermal Circulation, Ice Melt and Basalt Alteration
With physical processes similar to terrestrial seafloor hydrothermal systems, martian hydrothermal systems may provide a mechanism for transporting water, chemicals, and energy to the surface. These systems could shape surface morphology and may provide favorable environments for biological processes. Here we model a sill intrusion beneath a layer of basaltic rock and ice and investigate the melting process, induced fluid circulation and resulting rock alteration minerals. These models improve upon previous investigations by considering heat transfer through both conduction and convection. Results indicate fluid flow rates at ∼0.1 km3/yr for a 1 km2 sill surface area. This flow rate is much lower than those estimated for forming surface features; however, the melt water could be stored until the ice layer melts through and releases a large volume of fluid over a short time.
Hydrothermal rock alterations within the melt layer are also investigated. The model suggests that higher temperature alteration minerals such as chlorite, actinolite, and epidote would tend to form first at depth, whereas low temperature zeolites and clay minerals would form near the top of the ice melt zone. With increasing time, convection within the melt layer will cause the temperature to decrease and the low temperature alteration products will overprint or replace the high-temperature alteration minerals. Observation of these altered mineral layers would be evidence of hydrothermal activity and may also indicate ideal locations to search for evidence of life on Mars.
Social Implications of Astrobiology
Since the first detection of an extrasolar planet in 1992, Astronomers have discovered over 529 extrasolar planets, and this number will most certainly be outdated by the time you read this sentence. Before knowledge of extrasolar planets became a common place in society the average person was not subjected to facts of other solar systems, or even other earths. Thanks to the advancement of extrasolar planet detection technologies the discovery of Earth-like planets will surely be a common place in the media in the upcoming decades. In turn, the idea of life on other planets will become more realistic and less science fiction, even more so as advancements are made in the spectral analysis of exoplanetary atmospheres and surfaces. In the event that extraterrestrial life is detected, a wide range of human social groups will be affected including the views and cultures, generations and religions. I will examine the sociology of Astrobiology, focusing on the search for extraterrestrial life (both primitive and intelligent) and its social implications (from the microscopic to the macroscopic level of agency) as well as the ethics of messaging to extra-terrestrials. I will also include a small case study examining the views of an international group (representing 25 nationalities) of roughly 60 Millennial generation (generation X and Y) students of how their belief system will be affected in the case of life detection.
Astrobiology: Virus Evolution and Biogeography
Viruses are simple, yet highly evolved and efficient biological organisms. Molecular virology provides a means of understanding the persistence and evolution of rudimentary replicative systems and may thus provide insights into the characteristics of proto-life. Although viruses are known to be the most abundant organisms on Earth, their collective evolutionary history, biodiversity, and functional capacity are not well understood. Therefore, we are investigating virus diversity in Boiling Springs Lake (BSL): a large, acidic hotspring (pH 2.5, 55–95°C) located in Lassen Volcanic National Park, USA, which supports a relatively simple microbial ecosystem comprised of Archaea, Bacteria and several species of unicellular Eukarya. To identify viruses in BSL we extracted and sequenced DNA from virus-sized particles (<0.2 μm) isolated from 20 liters of BSL sediment. The vast majority of the ca. 380,000 sequences obtained do not match any characterized sequence in the public databases, and only 0.6% are identifiable as viral. Three Microvirus genomes have been fully reconstructed from a small subset of the viral sequences. Microviruses are among the simplest viruses known and are all remarkably similar despite their broad diversity and global distribution. Consequently, we have been able to investigate specific viral adaptations in response to local extremes of the BSL environment, and demonstrate phylogenetic relationships amongst BSL and other Microviruses. To discover completely novel viruses and address global virus biodiversity, we are attempting to determine whether the unidentifiable sequences denote common, yet uncharacterized environmental viruses, or whether they are derived from viruses unique to BSL.
The Astrobiology Primer v2.0: An Early-Career Astrobiology Project
The Astrobiology Primer is an introductory text, designed to give newcomers to the field a brief, but comprehensive, introduction to astrobiology that is longer than a review paper but shorter than a textbook. The primer grew out of the AbGradCon community, and like AbGradCon, it is a project conceived and run by and for early-career astrobiologists (graduate students and post-doctoral scientists). The original primer was published in 2006 in Astrobiology and was widely welcomed. The two of us are the Co-Lead Editors of the second edition. We are updating the primer to take account of new developments, and we are also completely re-writing the text using a more holistic approach. Our main goal is to produce something that is useful to other early-career astrobiologists, but we hope it will also be used more widely in education and outreach. It will be freely available to all online. We hope the primer will not only be useful, but will also be fun to read, and that it will convey our excitement and enthusiasm for astrobiology. An added benefit is that the process of writing the primer is, in itself, a way to strengthen the international early-career astrobiologist network as our team of volunteers covers 11 different countries in Europe, North America, South America, and Australia. At AbGradCon, we will discuss the community's progress on the primer, and preview its content and plans for publication.
Astrobiological Implications of the Radical AdoMet Enzyme HydG in Promoting Organic Proto- Biomolecule Diversity in the Prebiotic to Biotic Transition on the Early Earth
Iron-sulfur (Fe-S) clusters in enzymes can be viewed as highly tuned mineral catalysts that may provide insight into catalysis central to the prebiotic to biotic transition on the early Earth. By understanding the chemical reactions of Fe-S cluster catalysts in biological systems, structural determinants in the transition between these stages can be postulated. As a model system, [FeFe]-hydrogenases perform the catalytic reduction of protons to dihydrogen at the catalytic “H-cluster,” a highly tuned organometallic cluster containing iron and sulfide as well as carbon monoxide, cyanide, and a nonprotein dithiolate ligand. Biosynthesis of this cofactor requires a scaffolding protein (with a GTP-binding domain) as well as two radical S-adenosylmethionine (AdoMet) enzymes. Recently, we have shown that the radical AdoMet enzyme HydG catalyzes cyanide and carbon monoxide ligand formation from the decomposition of an amino acid at an Fe-S cluster. Together, these results provide a basis for understanding the diverse reactivity of iron-sulfur clusters and radicals, reactivity that may have been important in the prebiotic conditions on the early Earth. More specifically, this work provides insights into the potential for prebiotic Fe-S/radical chemistry to catalyze the modification of Fe-S minerals to produce new catalytic activities that may have been involved in the initial conversion of atmospheric gases required for the emergence of life.
Microbial Permineralization in Phanerozoic Gypsum Deposits: High Potential Target Rocks for Astrobiology Objectives
The search for an extant and/or ancient martian biosphere relies heavily on the selection of environments and mission sites that are likely to preserve indications of life. The focus of site selection for future missions has recently shifted towards phyllosilicates and away from sulfates as target rocks, despite the presence of large sulfate deposits at the martian surface. It is widely assumed that sulfates, much like carbonates, do not preserve microorganisms within crystals during growth and are therefore not desirable target minerals for future study. However, our current work, which focuses specifically on gypsum deposits, has demonstrated that gypsum crystals both trap and preserve microorganisms during growth, and commonly do so in a manner that results in the preservation of large microbial populations. Samples from various geologic ages and locations have been examined including: Permian (∼300 Ma) samples from the Delaware Basin, Texas; Miocene samples (∼7 Ma) from the Vena del Guesso Formation, Italy; and modern gypsum crystals from hypersaline environments in Australia, Baja, and Peru. All ancient samples contain demonstrably permineralized microorganisms, whereas modern samples illuminate a common mechanism of preservation and provide a potentially useful tool for determining both the rate of crystal growth and the paleo ‘up’ direction of such deposits. The markedly high frequency of preservation observed in terrestrial examples, combined with the potential ease of obtaining gypsum samples on Mars, since they are surficial deposits, strongly suggests that gypsum should be reconsidered as a high priority target rock for future martian astrobiology studies.
Ancestral Reconstruction of Synthetase Paralogs: Inferring Ancient Events in Genetic Code Evolution
Aminoacyl-tRNA synthetase (aaRS) protein families specific for each amino acid diverged early in life's history, before the time of the Last Universal Common Ancestor (LUCA), around 4 billion years ago. The co-evolutionary model of the genetic code suggests that these divergences either added new amino acids (neofunctionalization) or increased specificity between very similar amino acids (subfunctionalization). Each of these hypotheses can be tested using ancestral sequence reconstructions from existing genomic data, as neofunctionalization predicts that one cognate amino acid will be absent within the sequence of reconstructed pre-LUCA paralog ancestors, while subfunctionalization predicts the ancestor will contain an overabundance of sites with ambiguous likelihood for either cognate amino acid. Homogeneous and nonhomogeneous ancestral reconstructions were performed on alignments of tyrosyl-tRNA (TyrRS) and tryptophanyl-tRNA (TrpRS) synthetase protein sequences from 112 species, as well as 100 sets of simulated sequences. Amino acid usage rates, joint probabilities, and the degree of ambiguity between cognate amino acid pairs were all subsequently calculated from the probabilistic reconstructions. The reconstructed paralog ancestor of TyrRS and TrpRS contains no Trp, with a low joint probability (14.8%), a significant result supported by simulation studies. In contrast, analysis of aliphatic amino acids (Ile, Val, Leu) shows that sites reconstructing to either Ile or Val grow increasingly ambiguous approaching the pre-LUCA paralog ancestor (65% ambiguous, vs. 23% in domain ancestors). These results provide novel, compelling empirical evidence in support of the co-evolutionary model of genetic code, which is shown to include both neofunctionalization and subfunctionalization events.
The TIM Barrel Fold, Early Life Forms, and the Nature of Biological Complexity
The triosephosphate isomerase (TIM) barrel protein fold is thought to be present in a whopping 10% of all modern enzymes. The canonical TIM barrel architecture has a low secondary structure complexity, eight repeats of one alpha helix and one beta strand, and a low tertiary structure complexity, one outer ring of alpha helices and one inner ring of beta strands. In contrast to its structural simplicity, the TIM barrel architecture is known to catalyze five of the six major categories of enzyme function defined by the Enzyme Commission. Due to the location of their active sites, TIM barrel domains may acquire new functions with few amino acid changes and without disturbing the structural integrity of the fold architecture. The low structural complexity and vast functional diversity of the TIM barrel fold (as well as the non-random intron positions of some triosephosphate isomerase genes) led Walter Gilbert to propose that the fold was originally derived from a group of simple genes each encoding 15–20 amino acids, the products of which combined to impart a catalytic function. More recent bioinformatics-derived evidence supports an early, single origin of at least the majority of TIM barrel protein domains. Here, I explore the likely fundamental roles of TIM barrel folds in the genetic systems, metabolisms, and membranes, of early life forms as well as the astrobiological implications of a low complexity molecular structure yielding such a vast array of molecular functions.
Cryomicrobiology of the Upper Dry Valleys, Antarctica
The Upper Dry Valleys of the Antarctic are an important and unique analog for the polar regions of Mars since they are the only place on Earth where there is a layer of dry soil overlaying permanently frozen ground (permafrost). Similar to the martian atmosphere, the air is very dry and the ice-table depth is governed by water vapour diffusion, rather than liquid water. This site is interesting microbiologically because Antarctic permafrost can preserve a high number and diversity of viable cells over geological timescales, in addition to being considered an analog to the extreme martian environment. I am examining the potential for the upper Dry Valleys of the Antarctic to support microbial life at subfreezing temperatures. The major focus will be to determine if indigenous microorganisms are active at sub-zero temperatures (0 to −25°C) and form an active ecosystem in situ, or alternatively, are dormant microbes frozen in time. Here I will discuss preliminary results about the biomass, culturability, and microbial diversity of the Dry Valleys, as well as the acetate mineralization rates observed in these samples at sub-zero temperatures.
Origin and Evolution of Biological Nitrogen Fixation
The availability of fixed sources of nitrogen is thought to have impacted the evolution of life on Earth. The advent of biological nitrogen fixation facilitated the proliferation of life as abiotic sources of fixed nitrogen presumably dwindled. The ability to fix nitrogen is distributed widely among the bacteria and in the methanogenic Archaea. Here we report an in-depth phylogenetic examination of proteins required for biosynthesis of the active site cofactor in molybdenum (Mo)-nitrogenase. Gene duplication and fusion events revealed that Mo-nitrogenase is unlikely to have been associated with LUCA, but rather likely emerged in the methanogenic Archaea.
To better understand the constraints that may have facilitated the origin of Mo-nitrogenase and that likely impacted its subsequent evolution, we designed degenerate primers targeting the known diversity of the nitrogenase protein-encoding gene (nifH) and applied these in PCRs with DNA recovered from geochemically diverse thermal features in Yellowstone National Park. Phylogenetic and statistical analysis reveals that the phylogenetic structure of nifH is influenced by both geographical and ecological constraints. nifH genes were detected in acidic, high temperature environments previously unknown to harbor diazotrophic microorganisms. Acetylene reduction, selective enrichment, and 15N2 incorporation assays suggest the presence of active N2 fixing populations in several high temperature acid springs. Ex situ enrichment assays indicate these populations are specifically adapted to local conditions. These studies provide new insight into the environmental constraints that underpin the distribution, diversity, and activity of diazotrophs in geothermal environments and expand our understanding of the habitable zone of biological N2 fixation.
Conformational Evolution: Using Self-Assembling Peptides to Create Diversity
In the prebiotic planetary environment, many of the molecules present to participate in chemistry would have been quite simple, such as methane gas and dimethylformamide. In the Miller-Urey experiments, it was shown that through atmospheric events like an electrical discharge, these simple molecules could form amino acids. Cycling events involving heat, such as a change from day to night as a planet turns on its axis, are proposed to create a favorable environment for simple condensation reactions that would result in amino acids coupling together to form short peptides. We have shown that short peptides of different sequences have the ability to self-assemble into larger macromolecular structures with charged surfaces. These structures not only have their own unique surface properties but these properties can be changed by mixing short peptides of different sequences. Changes in the energy landscape during mixing contribute to creating a nucleus capable of producing a variety of structures within the same sample pool that are thermodynamically stable. Using these short sequences we have shown that we can create a diverse array of structures, each with a different surface chemistry. We have shown that these self-assembled structures are able to bind small molecules and perform catalysis, and propose that these properties would allow for a larger library of more complex biomolecules needed for information transfer and energy storage, such as nucleic acids and lipids. This ability to create diversity is essential in understanding how prebiotic molecules would be able to evolve under selective pressure.
The Drake Equation: Origins, Evolution, and Application to Astrobiology
Precursors to the Drake Equation have existed in various embryonic forms. However, it was the proposed construction of the Arecibo radio telescope antenna in 1958, initially intended to study Ionospheric backscatter, which motivated a meeting of the Space Sciences Board of the National Academy of Sciences. They recognized that an antenna of this size, when coupled to a transmitter of modest power (few 100's of kW), would allow two-way communication to be established with a similar setup anywhere in our galaxy. Since the inception of the Drake Equation in 1961, a number of significant discoveries have occurred that influence each of the variables that makeup this equation. From an Astrobiological perspective, for example, the growing recognition that life is established very early in Earth's history, and can be found in increasingly extreme environments, allows for an expanded range for potential extraterrestrial habitats. Some of the Drake Equation variables, which were simply an educated guess for most of its 50-year history, have become better defined. The discovery of over 500 confirmed exoplanets is just one example. Both transits and direct spectroscopic analysis provide opportunities to detect biosignatures in the atmospheres of terrestrial “Earth-like” exoplanets in habitable zones. Various potential biosignatures are considered, as well as problematic pseudo-biosignatures, which could be detected over interstellar distances. Given the radio telescope (and now optical SETI) bias of the original Drake Equation, and the discoveries since its inception, we consider some modifications to this equation to reflect this new understanding.
CYANOSPACE: Cyanobacteria from Extreme Desert to Space
Rock-inhabiting cyanobacteria belonging to the genus Chroococcidiopsis are studied worldwide for their tolerance to extreme environments such as desiccation, cold and radiation. Ground-based experiments were conducted on two strains of Chroococcidiopsis in order to study the survival of cyanobacteria to simulated space and Martian conditions, such as vacuum, sudden temperature changes, high UV radiations or high CO2 atmosphere levels. The two strains, isolated from porous rocks in the coastal desert of Chile (CCMEE 123) and in Beacon Valley, Antarctica (CCMEE 134), which are considered the closest terrestrial analogs of two Mars environmental extremes, were exposed as dried multilayers, overlain by a 3 mm Antarctic sandstone covering, to extreme environments in order to investigate their protection and repair mechanisms. This investigation was conducted by evaluating the colony-forming ability, the subcellular integrity of single cells based on membrane integrity molecular and redox probes, and the photosynthetic pigment autofluorescence. The genomic DNA integrity was also assessed by a PCR-based assay. The results showed a difference in protection ability under simulated space and Martian conditions in the two strains. Namely, the one isolated from the hot desert (CCMEE 123) showed a better recovery ability than the one isolated from the frozen desert (CCMEE 134). The former recovered its colony-forming ability and managed to maintain subcellular integrity avoiding or repairing DNA damage upon rewetting, while the latter completely lost its ability to form a colony. Therefore the former has proved to be an interesting sample for further study.
How to Build a Tricorder: Developing Quantitative Habitability Prediction Tools for Planetary Exploration
Habitability of planetary environments is considered a principal theme in astrobiology. Over the past decade, planetary exploration has centered on a “follow the water” strategy in the search for evidence of extinct or extant extraterrestrial life. This approach has focused astrobiological efforts for Mars and has produced a collection of appealing targets for future missions. However, merely following the water does not necessarily provide the full picture of habitability. The presence or absence of water and other constituents considered critical for life is simply a binary indicator of habitability that allows for delineation between habitable and non-habitable environments but results in an overabundance of “target environments”. Given the current mission constraints, it is unlikely that all habitable targets will be investigated with the scrutiny required to definitively determine evidence of life. Therefore, a more discriminating methodology is needed to optimize selection of target habitable environments. Here we present a habitability prediction tool concept that, when coupled to in situ geochemical measurements by instruments already used in planetary exploration, could optimize selection of the best samples for further in situ astrobiological analysis or for sample collection and return.
Holographic Microscopy: a Tool for Detecting Mobile Microorganisms on Europa
A digital holographic microscope (DHM) has been constructed for astrobiological exploration of Europa. It is rugged and submersible. It consists of a laser, a pinhole, a sample chamber, and a digital camera. The DHM does not form optical images. Instead, it records the interference between scattered (by the object) and unscattered beams as a hologram. The hologram (concentric rings) is saved on a computer and later used to reconstruct the size and shape of the object. Holograms can be acquired quickly, five per second, allowing for study of motility. We first tested the DHM with Euglena, a single-celled, motile green alga. The oval-shaped organism swims in a spiral path that changes direction constantly. We then studied a sample of sulfur bacteria. The 1.5 μm coccus swims and tumbles, forming a three-dimensional random walk. Last, we submerged the DHM in two lakes and observed a 6 μm motile rod and a single-celled, Euglena-like alga. In contrast, non-motile organisms, sediments, and air bubbles move in simple patterns, controlled by gravity or bouncy. These results suggest that holographic microscopy could be a powerful tool for detecting microorganisms on Europa and in other extraterrestrial aquatic environments.
Water on Early Mars
There is ample evidence suggesting that the conditions on early Mars differed from what we observe today. Hydrated minerals and geological structures suggest that some type of precipitation must have occurred early on in Mars' history. However, it is unknown to what extent liquid water was stable on the surface. Several theories exist, spanning the range from a global ocean to rather dry and cold conditions. Depending on these conditions, Mars could have been more habitable than today. In order to make any quantified statements, it is however necessary to constrain the environmental conditions. We use parameterized models of the thermo-chemical evolution to investigate the influence of volcanic outgassing of water and carbon dioxide. These models treat the production of crust and the concentration of gases in the melt in a self-consistent way. Model parameters have been chosen to specifically be compatible with many observational constraints, for example, the crust formation history and the measured concentration of radioactive elements. Our calculations unveil a picture of a rather cold and wet young Mars. Volcanic outgassing of CO2 amounts to 300 mbar, which is hardly sufficient to sustain liquid surface water by the greenhouse effect of CO2 alone. On the other hand, a substantial amount of water can be outgassed, leading to a 14 m thick global surface layer. Therefore, we suggest that water had crystallized and snowed down. When the surface temperature raised locally, e.g., due to nearby volcanoes, this ice layer melted suddenly, leading to transient liquid surface water.
Rapid Bacterial Spore Detection by Time Gated Luminescence
Bacterial spores are among the toughest known life forms, and have the ability to withstand a wide variation of extreme conditions including those found in space. This makes them of great interest to astrobiology from both the point of view of protecting other planets from contamination, and as a potential seed of life in the solar system. The typical method for measuring the number of viable spores is through culturing, a relatively slow method requiring 24–72 hrs. Our lab has developed a more rapid method that detects the spores as they germinate on the 10-minute time scale and return to a metabolically active state. During germination, spores release large amounts of dipicolinic acid (DPA), which can be bound by a terbium ion to form a long-lived luminescent complex. Using a time-gated camera with a pulsed UV light source, individual spores can be imaged, and followed in time as they germinate. This rapid detection method is being developed as a portable automated instrument for sterility assurance purposes. In addition the ability to detect single spores has allowed very sensitive measurements of returned environmental samples, such as Greenland ice core and Atacama Desert soil. Recently we have measured the total number of spores present, not just the germinable ones. Comparing the two populations determines the viable fraction of spores in a sample. A viable fraction measurement controls for variations in spore concentration across different environments, and allows better comparison of pore durability under varied environmental stresses.
Once in a Pale Blue Dot: Simulated Observations of an Extrasolar Earth-Moon System
The inability of the Moon to efficiently circulate energy from its dayside to its nightside leads to large surface temperatures on its illuminated hemisphere. As a result, the Moon can contribute a significant amount of flux to spatially unresolved infrared (IR) observations of the Earth-Moon system, especially at wavelengths where Earth's atmosphere is absorbing. We have paired the NASA Astrobiology Institutes Virtual Planetary Laboratory three-dimensional spectral Earth model with a model of the phase dependent IR spectrum of the Moon to investigate the effects of an unresolved companion on observations of Earth-like extrasolar planets. For an extrasolar Earth-Moon system observed at full phase at IR wavelengths, the Moon consistently comprises about 20% of the total signal, approaches 30% of the signal in the 9.6 m ozone band and the 15 m carbon dioxide band, makes up as much as 80% of the total signal in the 6.3 m water band, and more than 90% of the signal in the 4.3 m carbon dioxide band. These excesses translate to inferred brightness temperatures for Earth that are too large by about 2040 K, and demonstrate that the presence of an undetected satellite can have a significant impact on the spectroscopic characterization of terrestrial exoplanets. We show that, by differencing IR observations of an Earth with a companion taken at both gibbous phase and at crescent phase, Moon-sized satellites may be detectable by future exoplanet characterization missions for a wide range of system inclinations.
Shallow Subsurface Water on Europa?
Chaos terrain is unique to the surface of Europa, and thus may be diagnostic of the dynamic ice shell that gave rise to it. Chaos features like Conamara Chaos are characterized by large iceberg-like blocks and rafts of broken-up older surface material entrained in a dark hummocky background matrix. Such features are suggested to be sites of recent activity, fluidization, and exchange between the deep ocean and the surface. However, previous work has not been able to satisfactorily explain why chaos features are generally raised tens to hundreds of meters above the surrounding terrain. We will show that the physics that governs ice melt, hydrofracture and brine infiltration on Earth better explains observations of chaos terrain than formation by complete melt-through of a thin shell or warm ice diapirs. As shallow ice melts due to rising thermal plumes, deflection of the surface propagates surface cracks downward, allowing for vertical injection of water into shallow fractured or porous ice and for the ice to disrupt. Subsequent freezing of this trapped material can explain the heights of chaos features. More importantly, such a model argues for pervasive melting within the upper few km of the ice shell. Such a result is critical for understanding how Europa's ice shell overturns and determining the location of subsurface water. Not only might such shallow water be suitable habitats for life, but lenses may also be accessible by future landers even if the ice-ocean interface is much deeper.
LIBS for Extraterrestrial In Situ Investigation of Biological Materials
Laser-induced breakdown spectroscopy (LIBS) is an emission spectroscopy technique that can be applied for the investigation of geological surfaces. With the ChemCam instrument on the Mars Science Laboratory (MSL) to be launched in 2011 LIBS will be applied for the first time for in situ analysis on a planetary mission. Also other missions with LIBS instruments on board are proposed, including missions to the Earth's Moon, Venus, and asteroids. LIBS permits rapid multi-element analysis and relies on ablating material from the sample by focusing radiation from a pulsed laser onto its surface. Given sufficient laser energy, a small luminous plasma is produced. The emitted photons, which feature characteristic wavelengths of the elements composing the sample, are collected and analyzed spectroscopically. Thus, the elemental composition of the investigated material is obtained.
The investigation of biological materials with LIBS is of prime interest and has been studied in particular for extraterrestrial applications. In the present study pressed samples of martian analogue material were prepared with different microbiological content (one species of archaea, one species of bacteria). Applying multivariate analysis (MVA) such as principal component analysis (PCA), the ability of LIBS to discriminate the biological samples from the pure martian analogue soil was investigated under martian conditions. The complexity of elements in the soil complicates analysis, however, with sufficient statistics (accumulation and averaging of spectra) discrimination is possible.
A Search for Extraterrestrial Intelligence in the Kepler Field
In February 2011, it was announced that the Kepler Transiting Planet Survey had identified 54 planet candidates located in or near the so-called ‘habitable zone,’ the region around a host star where liquid water could exist on a planet's surface. Many of these planet candidates are just marginally larger than the Earth. In March of 2011, we will look for evidence of intelligent extraterrestrial life in this population by searching it for radio sources indicative of an engineered origin. Our search will include both targeted observations of known Kepler Objects of Interest (KOIs) and a raster scan of the entire 105 sq. deg. Kepler field. This search will be conducted using the 100 meter Green Bank Telescope, the most sensitive single dish radio telescope on the planet capable of viewing this field. Baseband voltages will be recorded over a 400 MHz band centered at 1.4 GHz and will be searched using the distributed computing projects SETI@home II and AstroPulse. Here we will discuss the search methodology, observations and early results. A broader discussion of SETI science will be included to provide context for the current work.
60Fe-60Ni Systematics of the Angrites: Implications for the Initial Solar System Abundance of 60Fe
The meteoritic record preserves evidence of the existence of a number of short-lived radionuclides in the early solar system that are now extinct. One of these radionuclides, 60Fe (half-life 2.62 Ma), is of particular interest because it can only be formed by stellar nucleosynthesis processes, and therefore can provide important information about the astrophysical environment the Sun formed in. The energy from the decay of 60Fe might also have been an important heat source for the melting and differentiation of small asteroids and planetesimals in the early solar system. Additionally, 60Fe could potentially be used as a high-resolution chronometer for geologic events in the early solar system. The abundance of 60Fe in the early solar system is currently not well constrained with current estimates of the initial solar system 60Fe/56Fe ratio ranging from ∼10−8 to ∼10−6. In order to better constrain the initial solar system abundance of 60Fe, we have investigated the 60Fe -60Ni isotope systematics of a group of basaltic meteorites, the angrites. We measured Ni isotope ratios and Fe/Ni ratios in bulk samples and a pyroxene mineral separate from the D'Orbigny angrite using inductively couple plasma mass spectrometry. All the samples have excesses of 60Ni, relative to the terrestrial abundance, that correlate with their Fe/Ni ratios, indicating the presence of extant 60Fe when D'Orbigny formed. The age difference between D'Orbigny and calcium aluminum rich inclusions (CAIs) is well defined and allows us to estimate a precise initial solar system 60Fe/56Fe ratio of ∼1 × 10−8 (i.e., when CAIs formed).
Dune Morphology and Substrate Dependence on Titan
We are using Cassini's Visual and Infrared Mapping Spectrometer (VIMS) to study Titan's sand. Specifically, we are constraining the sand's composition, the precise composition of which is still unknown, and its graphical distribution. Water ice has been ruled out, leaving atmospherically-derived hydrocarbons as the best fit. We spectrally unmixed chosen pixels, each representing one unique composition, to determine the composition of Titan's equatorial sand seas. We selected our spectral endmembers using high resolution VIMS IR images (noodle maps), specifically from the flyby T20. We have 5 spectral endmembers, labeled by color from VIMS IR maps: dark brown, dark blue, Xanadu bright, equatorially bright, and 5-micron bright. The exact superposition of spectral endmembers of the sand's composition remains the subject of further study. We set up a linear model to test on mixed substrate pixels from the T20 flyby of Cassini over the northern Fensal sand dunes. Our model assumes some percent dark brown (sand) and some percent one other endmember. The product is a substrate map of Titan's dune fields, which we will compare with RADAR maps of the same area. Our results will determine if substrate type plays a role in dune morphology and location. The Titan biosphere and active hydrologic cycle make this moon a prime site for astrological studies. The hydrocarbon dune fields analyzed here provide a potentially important concentration of surface organic material that, when mixed with liquid water via cryovolcanism or impact melting, could lead to potentially habitable environments.
Collective Dynamics, Functional Evolution, and the Emergence of Life
A defining feature of life is the collective behavior of biological systems: no single molecule of an organism is alive, yet an organism as a whole is living. Additionally, natural selection, a pinnacle feature of Darwinian (biological) systems, requires diversity. Therefore it is likely that the first living systems emerged a collective property of a diverse population of coexisting informational replicators. However, achieving a dynamically stable and diverse population of potentially competing template replicators remains a challenge for realistic models of emergent life. Catalytic closure (e.g., hypercycles) is one solution, but leads to difficultly as it is unlikely that such complex networks of autocatalytic feedback could emerge en masse on the prebiotic Earth. Moreover, such systems are highly unstable to parasitic behavior. Here a different approach is taken, by appealing to environmental coupling to replicator dynamics, a model is presented demonstrating that environmental feedback may have been a major driver in generating and stabilizing prebiotic diversity. The model presents a framework for prebiotic evolution in which regular environmental fluctuations (i.e., day-night cycles) drive polymer formation, replication, and degradation. Differentiation in replication rates occurs dynamically as a result of local variations in monomer population density, introducing a dynamic fitness landscape corresponding to local environmental conditions. Tracking population diversity and spatial organization, the emergence of collective behavior is observed. Moving through parameter space, system evolvability is explored within the context of the emergence and propagation of novel function. The implications of this work and future directions are discussed.
Geobiology of Acid-Saline Systems: Evaluating Mars Analogous Biosignatures
The weathering of sulfur and iron minerals has been integral to developing martian surface conditions during the last 3.5 billion years. Acid-saline terrestrial gossans (oxidized rock) provide an important analog for understanding how these minerals weathered on Mars. Microbes can change the environment around these minerals, leaving behind distinct biosignatures. Therefore, they comprise a model system for biosignature preservation that is relevant to early martian conditions. This study investigates the role of biology in acid-saline mineral weathering and biosignature preservation in gossans. This work will create a catalog of mineralogic biosignatures that can provide guidance for interpreting features observed by Mars Science Laboratory (MSL).
Filaments and spores have been observed in analog rocks. Morphologically, most are putatively fungal (≥5 μm diameters, compared with documented hyphal structures), while others are putative bacterial filaments (1–3 μm diameters). Bacterial and fungal filaments are either bare or coated with goethite. Fungal filaments appear typically unattached to substrate, and bacterial filaments can be attached or span voids. The resolution required to identify these communities is higher than the resolution of the MSL instrument MAHLI (MArs Hand Lens Imager), at 13.9 μm/pixel. Composite structures may be resolvable, but not individual organisms. Polymerase chain reaction confirms the presence of eukaryotic, bacterial, and archaeal domains.
The characterization of these microbial communities will provide an important catalog of mineralogic biosignatures MAHLI can observe. With this data, the MSL science team will be prepared to recognize these biosignatures on Mars, initiating opportunities for missions to the red planet in search of extraterrestrial life.
Preliminary Results from a Three-Dimensional Climate Model of the Archean
Over the past two decades, studies of the early climate have typically used one dimensional radiative-convective climate models that contain numerous simplifications. Here we present preliminary results from a coupled three-dimensional climate model of the Archean Earth. The model is based on the NCAR Whole Atmosphere Community Climate Model (WACCM). The radiative transfer code has been updated with a new correlated-k distribution model that has been validated against line-by-line calculations for H2O, CO2, and CH4 absorption. The model incorporates a fractal hydrocarbon haze layer utilizing the Community Aerosol and Radiation Model for Atmospheres (CARMA). The model also takes advantage of WACCM's interactive cloud and sea ice schemes. Previous models of the Archean have ignored both cloud and ice feedbacks, instead prescribing an elevated but fixed surface albedo for all atmospheric states (3). However, changes in both sea ice coverage and clouds are likely to be just as important as solar luminosity changes and atmospheric composition changes in affecting the surface temperature of the Earth. The lack of interactive clouds in earlier models has also resulted in an overestimation of the radiative forcing due to increased greenhouse gas concentrations. This new model will provide a detailed view of the complex coupled climate processes of the Archean and yield give new insight into the faint young Sun paradox.
AbGradCon 2011 Poster Presentations
Astrobiology Outreach Through Space-Based Disaster Management Education
The idea of what constitutes a space program is undergoing a quiet but incredibly rapid worldwide revolution. New space programs are being established all over the world, and existing programs are being expanded, to address the pressing challenges of disaster preparedness and response, resource stewardship, and climate change monitoring that can best be studied using space-based systems. This presents a unique opportunity for education and public outreach focused on raising awareness of the importance and benefits of space based research and astrobiology. Through the Safety From Above initiative facilitated by teacher trainers at Teachers Without Borders and scientists at Blue Marble Space Institute of Science, a series of space science lesson plans is being developed and tested. The lessons are designed to be conducted anywhere in the world with inexpensive and locally available classroom materials. The lessons emphasize space applications and how they affect and protect people every day, however, every lesson topic has a direct or indirect correlation to astrobiology education. Lesson topics include Stars, Planets and Moons, Satellite Altimetry, Space Debris and Impacts, Satellite Imagery, Global Positioning Systems, Atmospheres, and Orbits. The lessons are available for free download at
Remote-Sensing of Surface Characteristics on Cloud-Enshrouded Planets
To an extrasolar observer, Venus and Earth might appear quite similar due to their comparable mass, size and bulk compositions. This apparent similarity is preserved at UV and visible wavelengths where Venus' hellish surface conditions are hidden by a planet-wide, photochemically generated cloud deck. This highly reflective cloud deck produces an effective emitting mid-infrared temperature 30 K less than the Earth's. The 737 K Venusian surface is thoroughly veiled at these wavelengths. However, at near-infrared wavelengths, several “spectral windows” exist that allow us to probe all the way to the planet's surface, allowing more accurate characterization of Venus' true nature. To explore the Venus lower atmosphere and surface conditions we have obtained moderate spectral resolution (R = 3500) near-infrared (0.95–2.46 μm) spectra of Venus using TripleSpec on the Apache Point Observatory 3.5 m telescope. Observations of H2O in the lower atmosphere through near-infrared spectral windows will help to constrain the efficiency of the greenhouse. Quantification of water abundance and variability is also valuable to improve models of the Venus greenhouse mechanism. Simultaneous observations of SO2, HCl, and surface temperature may indicate volcanic outgassing on the surface and could bolster the claims of volcanism by the Venus Express team. O2 airglow in the mesosphere provides information on the atmospheric dynamics. Studying Venus' near-surface environment through these atmospheric windows will help inform us of the limitations inherent in remotely characterizing near-surface environments of cloud and haze-enshrouded exoplanets. Venus may represent a typical end state for habitable planets, so such information is astrobiologically salient.
The Origin of the Ribosomal Small Subunit
All life shares a universal genetic code, using very similar machinery to translate informational molecules (nucleic acids) into functional molecules (proteins). The ribosome is the center of the translation system and is composed of two macromolecular assemblies, the large (LSU) and small (SSU) subunits. While the LSU is responsible for protein synthesis, it is the SSU that enforces the genetic code.
A comparison of ribosomal sequence and structural data between bacteria and archaea/eukaryotes provides information about the Last Universal Common Ancestor (LUCA) and earlier for both the LSU and SSU. High-resolution X-ray crystallographic structures allow us to map Mg2+ interactions within ribosomes. Also, the primary structure (sequence), secondary structure (base pairing) and tertiary structure (conformation, long-range) interactions correlate with relative age. Using these correlations between structure and relative age, we extend and modify our modeling procedure to fit the SSU rRNA and certain ribosomal proteins.
We present a model for the origin and early development of the SSU. The most critical parts of the SSU, including helix 44 have a Mg2+ interaction pattern indicative of very early RNA, including a newly discovered Mg2+ micro cluster (μc), a motif. Based on protein and Mg2+ density, we propose that certain parts of SSU rRNA may be as old as certain parts of LSU rRNA, with the ancestral SSU being coopted from some lost function. Additionally, we propose a model for the ancestral SSU, which can be created synthetically for use in in vitro experiments.
Classification of Marine Microbial Biodiversity Using Digital In-Line Holographic Microscopy: A Life Detection Method for Aquatic Environments
If extant life, or even remnants of bacterial cells, is present within subsurface ocean of Europa, microscopic imaging represents one of the most sensitive and conclusive methods for its detection. It serves as a complementary method to instruments designed to detect extraterrestrial life by targeting chemical and metabolic biosignatures that risk being inconclusive. Submersible Digital In-Line Holographic microscopy (sDIHM) provides an operator-free method of 4D optical imaging with large depth of field and spatial resolution of less than a micron. The microscope objective focuses a laser beam at 405 nm onto a pinhole from which a spherical wave emanates to illuminate an object within a liquid volume. A geometrically magnified diffraction pattern is formed and stored on a CCD chip in the form of a hologram. A single hologram consists of optical cross sections containing dimensions, shape, identity and size of microorganisms and particles. This rapid and efficient technique maximizes our ability to explore inaccessible aquatic environments and aid in recognition of authentic biosignatures beyond Earth. During January 2011, sDIHM was deployed on a 19-day expedition across the Atlantic Ocean to investigate the marine microbial life of the open ocean environment. sDIHM visually inspected water samples collected from the ocean surface, towed nets, sargassum, biofilms on marine debris and at a depth of 200 m. This work will yield insight into the scales of variability in the types and abundances of species. High-resolution 3D reconstructions, morphometric analysis, and comparative studies using confocal microscopy will be presented.
Gas Phase Chemistry of Deprotonated Polycyclic Aromatic Hydrocarbons
Ion-neutral chemistry is an integral component in determining the evolution of the interstellar medium (ISM). The detection of fullerenes in the ISM suggests that polycyclic aromatic hydrocarbons (PAHs) may play an important role in the chemistry of dense clouds. The gas phase reactivity of phenide with molecules of interstellar relevance has been studied. In addition, reactions of deprotonated naphthalene and anthracene with H, H2, and D2 were investigated. The experiments were carried out using a flowing afterglow-selected ion flow tube (FA-SIFT). Reagent anions were generated by chemical ionization, mass selected by a quadrupole mass filter, and injected into the reaction flow tube. Stable reagent molecules were introduced into the reaction flow tube through a manifold of inlets and allowed to react with the reagent anions. Hydrogen atoms were produced by thermal dissociation of H2, and introduced at a fixed inlet. Ion signal intensities were measured using a quadrupole mass filter coupled to an electron multiplier. Reaction rates and product distributions were determined by monitoring the ion signal intensity as a function of atom concentration or reaction distance. Reactions of phenide with neutral molecules proceed through multiple mechanisms including proton abstraction, atom abstraction, and SN2 processes. Reactions of the deprotonated PAHs with hydrogen atom proceed exclusively through an associative detachment channel with, whereas reactions with H2 and D2 are extremely slow. The reaction rate constants and branching ratios measured in the current study provide reaction mechanisms and critical parameters for astrochemical modeling.
Using the Kepler February 2011 Data Release to Estimate the Frequency of Planets
NASA's Kepler mission is a space telescope designed to detect transiting extrasolar planets. Kepler monitors the brightness of over 100,000 stars for 3.5 years and looks for periodic dimming events indicative of a planet blocking the light from the star from reaching the spacecraft. In February 2011, the Kepler team announced the discovery of 1235 planet candidates. The majority of the candidates have radii smaller than Neptune and orbital periods less than fifty days. Although these data are preliminary and some candidates may prove to be astrophysical false positives, this sample of planet candidates is large enough to probe the underlying distribution of planets as a function of planetary radius, semimajor axis, and host star spectral type. We approach this problem by considering a variety of underlying distributions and assigning planets according to those distributions to the stars listed in the Kepler Input Catalog. We simulate the likelihood of detecting a transit of each planet around its assigned host star, accounting for the geometric probability of transit, the transit duration, and the number of transits that would be observed during the first year of the Kepler mission. We require a signal to noise ratio of 7 for detection as required by the Kepler team for inclusion in the list of Kepler Objects of Interest in the February data release, and we reject any underlying distribution of planets that differs significantly from the Kepler data.
Applying Cosmochemical and Geochemical Constraints for Exoplanet Habitability
In the search for habitable worlds beyond our solar system, the main considerations for whether an exoplanet is Earth-like are its size and orbital distance. The habitability of an exoplanet can be further constrained, however, by its current heat production rate from the long-lived, heat-producing radioactive isotopes 235U, 238U, 232Th, and 40K. As the products of supernova explosions, these isotopes had lower galactic abundances in the past. Their decay is currently the primary source of heat in Earth's interior, driving plate tectonics. Plate tectonics plays a key role in the carbon cycle on Earth, and without crustal recycling, a planet may not be habitable.
The discovery of Gliese 581g, the 3.1-M⊕ exoplanet whose existence is hotly debated, was so exciting because it was said to lie in its star's “Goldilocks Zone”. Gliese 581 is ∼8 Gyr-old star, which means that its terrestrial planets would have formed with lower abundances of the heat-producing isotopes than did Earth. Without enough heat being generated, plate tectonics, if initiated at all, could not be maintained for a significant period of time in these planets. Furthermore, being that Gliese 581 is significantly older than the Sun, the heat-producing isotopes in its terrestrial planets decayed to extinction long ago, shutting down their internal heat engines and halting plate tectonics. As such, even if Gliese 581g does exist, it is likely not habitable. We can generalize these cosmochemical and geochemical constraints to apply to all terrestrial exoplanets based on the age of their solar systems.
Multi-Edge XAS Study of Pyrite Surface Exposed to Hydrogen Plasma
Iron-sulfur (Fe-S) mineral surfaces have been implicated in activation of small, inert molecules to form chemical precursors for the building blocks of life. Understanding the structure and reactivity of Fe-S mineral surfaces is essential for evaluating the likelihood of these reactions. The synchrotron radiation-based, multi-edge X-ray absorption spectroscopic (XAS) technique allowed us to evaluate the geometric structure, oxidation and spin states, and ionic and covalent character of the Fe-S surface structure and reaction products upon exposure to a beam of hydrogen atoms. In this study, pyrite samples, prepared by beam-surface scattering experiments using a molecular beam of H/D atoms in Ar carrier gas with varied temperatures and exposure times, were examined. The XAS measurements were performed using three different detection methods: electron-yield, fluorescence, and transmission, providing information at different depths of 20–50 Å, 100–500 Å and 1000–5000 Å, respectively. The beam- surface scattering experiments of H/D atoms with the pyrite [100] surface unambiguously showed the formation of D2S, which close to exponentially decreased over time, indicating the near complete conversion of the surface-accessible sulfur atoms. Using electron yield detection, EXAFS showed the formation of a metallic Fe(0) surface layer. Using fluorescence detection, XANES indicated the formation of a reduced Fe-S layer, tentatively characterized by
In Situ Biodosimetric Experiment for Astrobiological Goal
Panspermia hypothesis is a well-known theory based on the view that life could exist and be transported in space for a long time in a dormant state. It is possible, that life-harbouring asteroids or comets could propagate life on sterile planets. The term exogenesis refers to this: life on Earth origins from somewhere else, for example planet Mars. To prove this theory it is necessary to investigate if simple organisms can survive space conditions, like large temperature changes, radiation and vacuum. Our experiment focuses UV radiation. The presentation will show the principles and applications of DNA and RNA based biological UV dosimeters developed by Research Group for Biophysics (RGB) for assessing the biological hazard of the living systems on the Earth's surface, in the hydrosphere, and in space environment, too. This concept was adapted as the part of the Expose-R platform, which was accommodated on the external pallet of the International Space Station (ISS), where the samples were exposed directly to the extraterrestrial solar radiation with different filters simulating different atmospherical conditions. Now we are working on a more advanced solution, which will make it possible to observe the dynamic properties of exposition processes by the application of in situ evaluation techniques.
Ammonia Formation on Iron Sulfide Surfaces Under Simulated Hydrothermal Conditions
A hypothesis in this research is that there may have been a transition period on early Earth where inorganic iron-sulfur clusters were adapted for use by the biological world. It has been proposed by others that prebiotic chemistry originated on the surfaces of iron sulfide surfaces within the extreme environment of hydrothermal vents (i.e., the “iron-sulfur world”). Currently, our studies are attempting to answer the question as to whether iron sulfide minerals doped with various biologically relevant Mo-based cubane structures can catalyze biologically relevant chemistry under a wide range of temperatures, pressures, and pH environments. In short, did this chemistry precede the chemistry that we now associate with Mo, V, Fe, and S containing enzymes (such as nitrogenase). Prior studies have shown that dinitrogen can be converted to ammonia in the presence of iron sulfide mineral surfaces under hydrothermal conditions, adding support to the “iron-sulfur world” hypothesis. Under current study is the conversion of NO,
Adsorption of L-Enantiomeric Amino Acids on Analog Meteoritic Material: The Potential Extraterrestrial Origin of Homochirality in Earth-Based Life
With the exception of some fungal peptides, all life on Earth uses L-enantiomeric amino acids exclusively. The reason for this is unknown and presents a keystone question in the origin of life field.
Meteorites have long been known to contain amino acids, both biological and non-biological. Recent work suggests some carbonaceous chondrites, CC, contain L-enantiomeric excesses of some amino acids. The largest excesses are found in low-temperature, aqueously altered CCs, such as Murchison and Orguiel. This suggests that meteorites with an excess of L-amino acids might have seeded Earth, and this bias was incorporated into living matter during the origin of life.
To investigate this, bulk adsorption experiments involving amino acids and analog meteoritic material are conducted. To represent pristine meteorites, unaltered olivine rocks are used. Fayalite and forsterite end-members were obtained from the Smithsonian Museum and will be mixed to obtain a Mg/Fe ratio near to that of the CCs. A near fully serpentinized rock from the Troodoos Massif Formation in Cyprus will be used to represent aqueously altered meteoritic material.
The amino acids chosen are glutamate and aspartate, 5- and 4-carbon amino acids that are well-characterized. To exclude enrichment via biological contamination, a five-carbon non-biological amino acid, isovaline, will also be used.
Preliminary results suggest a possible L-enantiomeric enrichment on the serpentinite, up to ∼10% for aspartate, and further investigation is ongoing to confirm this. If found to be real, this will yield insight into the origin of homochirality in Earth-based life.
Ion Desorption from Frozen CH4 and N2 After Irradiation by MeV Heavy Ions
Frozen N2 and CH4 (about 15 K) were bombarded by fission fragments from 252Cf (energy of about 65 MeV). The mass-to-charge ratio values of the sputtered positive and negative secondary ions were analyzed by time-of-flight mass spectrometry. Target surface was kept at ultra-high vacuum, therefore the frozen gas layer (CH4, N2, or mixtures of both gases) was continuously renewed. Spectral data indicated that clusters of positive ion compounds were families of
The Effects of the Acraman Meteorite Impact on the Evolution of Eukaryotes in the Neoproterozoic
The Acraman meteorite impact at the Gawler Craton, South Australia (c. 580 Ma) could be a major factor influencing the ecology and evolution of primitive eukaryotic alga in Australia. The estimated diameter of this condritic bolide was 4.8 km leaving a 85–90 km collapse crater. Such an event could have a catastrophic influence on the life in the Neoproterozoic; it has been hypothesised to be the trigger for rapid evolution in its aftermath. In this study, we use organic geochemistry to fill the gaps in the body fossil record. The extraction and identification of molecular fossils has been used to make far-reaching assumptions on the ecology and evolution on early life. In our last AbGradCon presentation, we showed that ∼75% of samples previously published in the literature had been infiltrated by anthropogenic contaminants and the data unreliable. By using our new techniques described previously we have been able to lift the shroud of contaminants to characterise the Neoproterozoic oceans of Australia through the Acraman impact ejecta layer to determine the effects on life in the oceans. A large hiatus in saturated biomarkers occurs for a few meters after the impact ejecta layer, which suggests a mass extinction event due to the impact. In this presentation we will show our new results, which show that in contrast to previously published literature, we identify striking trend from an ocean entirely composed of green algae to one dominated by red algae, which diversifies with age.
Iron-Sulfur Cluster Biosynthesis: The Transition from the Abiotic to Biotic Earth
Iron-sulfur proteins can catalyze different reactions that are essential to life such as carbon and nitrogen fixation. These Fe-S enzymes have similar features as the Fe-S minerals and their derivatives. By comparing physical and catalytic properties of Fe-S compounds found in both biological and geological systems, we are aiming to rationalize the transition between prebiotic and biotic earth. We are using the [FeFe]-hydrogenases enzyme as a model to examine the synthesis of complex Fe-S clusters in biology and whether its biosynthetic pathway can be related to modifications of Fe-S minerals. The [FeFe]-hydrogenases reversibly catalyzes hydrogen oxidation with an active-site termed the H-cluster, which is composed of a [4Fe-4S] cubane linked to a [2Fe] unit decorated by CN−, CO, and a bridging dithiolate ligand. The synthesis of H-cluster occurs via the stepwise modification of a FeS cluster by two radical SAM enzymes. Our recent studies suggest that one of the radical SAM enzymes is responsible for synthesis of the CO and CN− ligands from amino acid radical, which is a modern day example of ligand assisted autocatalysis and is believed to be a necessary process of prebiotic chemistry. The modified FeS precursor is transferred to the hydrogenase, making it catalytically active. This process of maturation argued to be similar to the nesting and specialization of metals and metal clusters reactivity. Our studies indicate that the active site of [FeFe]-hydrogenases is synthesized and nested in the structural protein via a set of reactions that can be compared with the prebiotic chemistry.
Centrosymmetric Molecules as Possible Carriers of Diffuse Interstellar Bands
We present the correlation between the width of some diffuse interstellar bands and the excitation temperature of C2, based on high resolution and high signal-noise ratio spectra. The excitation temperature was determined from absorption lines of the Phillips A-X and Mulliken D-X systems (toward eighteen objects). Here we show that the width and shape of some DIB's profile (6196A, 5797A) apparently depend on the gas kinetic and rotational temperature of C2, being broader for its higher values. There are also DIBs (4964A, 5850A) for which that effect does not exist.
Synchrotron-Based X-ray Techniques in Geomicrobiology and Astrobiology
Over the past several years the development of specialized analytical techniques utilizing X-rays from synchrotron sources has opened up many doors for researchers across a variety of fields. In both geomicrobiology and astrobiology, these techniques have enabled high-resolution geochemical analyses of mineralized features, such as biosignatures, in a non-destructive manner. Where previous techniques usually involved in-depth sample preparation, many of the synchrotron-based techniques can be used on whole samples in low to no vacuum, and even on samples that are wet, frozen, or in anoxic conditions. X-ray microprobe beamlines are specifically designed to offer both high spatial resolution for element mapping and high spectra resolution for spectroscopic analyses. This means that it is possible to make detailed maps of features at the sub-micron scale that not only show the distributions of different elements, but also differentiate the various oxidation states of redox-active elements. These techniques can be combined with additional micro-spectroscopy analyses and in situ micro-X-ray diffraction on heterogeneous samples to determine element coordination and mineralogy. I will discuss the utility of synchrotron-based X-ray techniques in geomicrobiology and astrobiology and give specific examples of the application of these techniques to my own work on the identification of biosignatures in subseafloor basalts.
From Methanogenesis to Anaerobic Oxidation of Methane: What Can a Terrestrial, Hypersaline, Cole Methane Seep of the Canadian High Arctic Tell Us About the Implications of Mars Methane?
On Earth, methane is often synonymous of microbial activity whether it relates to biological methanogenesis or to being an energy source for methane oxidizing microbes. On Mars however, the (astro)biological implications of recently monitored methane emissions are still unknown and under much debate. While future missions to the red planet will try to elucidate this mystery, another way to tackle this question, at least in some part, is to look whether or not such microbial processes are actually happening in terrestrial settings bearing analogous conditions expected to be found on Mars.
The Lost Hammer (LH) spring of the Canadian High Arctic so far accounts for the only known terrestrial methane seep in a cryoenvironment on Earth present in the form of a hypersaline (24% salinity), subzero (−5°C), perennial spring arising through thick permafrost. Considering geomorphic evidences implying the putative presence of shallow saline water channels and spring-like structures on Mars, the average cold temperatures of the martian surface, as well as recent martian methane detections, the LH spring represents a potential Mars-analogue environment. Genetic and microscopy analyses of its surface and channel sediments actually revealed the presence of both methanogens and members of the still poorly understood methane oxidizing archaea. Still, further analyses of the deeper, more anaerobic, layers of the LH spring are necessary to assess the still unanswered question of these microbes' viabilities and/or activities under such hypersaline and cold conditions; conditions which may well be present on our planetary neighbor.
Extracting Community Interactions from Microbialite Morphology: Cyanobacteria, Carbonate, and Environmental Change in Lake Joyce of the Antarctic Dry Valleys
Calcified microbial mats dominated by cyanobacteria are abundant in perennially ice-covered Lake Joyce, McMurdo Dry Valleys, Antarctica. Long-term growth of microbial structures occurred during lake level rise, and carbonate within these structures records cyanobacterial community shifts, providing insight into microbial response to environmental change.
The relative abundance of cyanobacteria morphotypes and mat morphologies vary with depth in Lake Joyce. Although photosynthesis is currently excluded below 12 m due to light limitation, cm-scale pinnacles, honeycomb, and prostrate mat are abundant from 7 to 20 m, and decimeter-scale calcified pillars are dominant from 20–22 m. Structures currently below the photosynthetic compensation depth are thus relics of former lake conditions more amenable to biomass accumulation. Documented lake level rise of ∼0.2 m per year over the last 35 years supports this interpretation. Relic structures from 20–22 m were collected to investigate changes in community composition and carbonate precipitation with increasing light-limitation. Intact structures were scanned using X-ray computed tomography to document transitional growth forms and calcification within the microbial structures. Scanned samples exhibit progression from columns with concentric calcified layers on the interior to discrete bracts with common apical calcified rods on the exterior. Carbonate from dissected structures has been morphologically characterized, and preliminary SEM data demonstrate that incorporated filament casts cluster with diameters from 0.5–1.3 and 3.2–6 m. Distinct diameters are consistent with separate cyanobacterial communities now present in different light environments of the lake. Results to date demonstrate the co-variation of community composition and style of carbonate precipitation within the changing environment of Lake Joyce.
Acid-Sulfate Weathering Pathways at Cerro Negro and in Experiments: an Early Mars Analog
Observations of Mars have detected sulfate in several locations. These deposits are thought to form through acid-sulfate weathering, but the specific environment may vary. One environment proposed is a volcanic setting with high-temperature, low-pH, and high-sulfur. To study this, we are employing methods of field work, laboratory experiments, and geochemical modeling. Cerro Negro, Nicaragua is an ideal analog due to its martian-like lithology and young, recorded history. Geologic and biologic field samples were collected during excursions by Drs. Hynek, McCollom, and Rogers. Solid products from the field and experiments are analyzed with XRD, SEM, and thin-section petrology. Fluid and condensed gas samples are analyzed with ICP. Secondary mineralogy at CN is largely Ca-sulfate, clays, silica, and iron oxides. The relative lack of Mg-, Al-, and Fe-sulfates indicates removal from the system. Dozens of enrichment cultures, taken from field locations of varying temperature and pH, have been successful for a range of microbes. Experiments and modeling are now being used to characterize the system, by reacting individual basaltic components at varying temperatures and fluid:rock ratios. Alteration occurs extensively even in short timesteps. Models using Geochemist's Workbench have aided in interpreting experimental results. For example, fluid chemistry and models showed that Mg-sulfate, despite being prominent in SEM images, should be undersaturated, leading to the exploration of Mg-sulfate as an evaporitic formation. Experiments varying fluid:rock have similar mineral type, but differences in size, abundance, and crystalline form. Understanding geochemical pathways will help constrain martian paleoenvironments, which in turn speaks to habitability.
Geomicrobiology of Rock Coatings from Kärkevagge, Swedish Lapland
Kärkevagge is a glacially eroded U-shaped valley in arctic Sweden. Characterized by a unique geochemical weathering regime, the microbial influence on weathering in the valley is poorly understood. We have investigated the abundant rock coatings in the valley, which exhibit great diversity in mineralogy and distribution, to understand the role of microbes in rock coating genesis. Isolating and amplifying 16S rDNA genes, we have been able to construct a clone library for a sulfate crust sampled in Summer 2010. The isolates from this sample contained close relatives to bacteria found at acid mine drainage sites. Such sites have been suggested as geochemical analogs for Mars bacterial isolates from Kärkevagge show their tolerance for heavy metals, low annual precipitation, high salinity, and low temperatures. While such bacteria are not the most extreme in any single environmental stress, their “jack- of-many-trades” survivability makes them of particular interest for astrobiology on Mars. In addition to the conditions in which these organisms can thrive, the nature of the rock coatings themselves are important, not only because they could provide a surface habitat on Mars protected from radiation, but also because of the their distinct morphologies. Should these rock coatings prove to be predominantly biological, they could be used as potential bioindicators on Mars, easily accessed by current and future rovers. Ultimately, this work seeks to determine the biogenicity of rock coatings and their potential as biosignatures.
Lago Infinito (Frasassi Caves, Italy) Microbial Communities as an Analog for Pre-Phototrophic Earth
Before the advent of phototrophy on early Earth, microbial life would have been limited to lithotrophic metabolisms, such as sulfate-reduction. By studying the metabolic capabilities of microbial communities that thrive in analogous environments, we can speculate on the challenges that would have faced our microbial ancestors. An unusual biofilm with ropelike morphology was recovered by divers from the anoxic and sulfidic water of a remote cave lake (Lago Infinito). The biofilm has high species richness with over 1/3 of the 16S rRNA metagenomic reads identified in clades with less than 2% representation. Deltaproteobacteria and Chloroflexi dominate the biofilm making up 33% of 16S rDNA metagenomic reads. Deltaproteobacteria in sulfate-reducing clades make up a significant percentage of the community, consistent with geochemical data and thermodynamic calculations showing that sulfate reduction is highly favorable. Chloroflexi in organoheterotrophic clades, Dehalococcoidetes and Anaerolinae, are also significant populations. BLASTx of metagenomic reads to the NCBI nonredundant database confirm the importance of Chloroflexi and Deltaproteobacteria, and highlight considerable database bias. In addition to dissolved organic carbon (5 M as acetate; >1 ppm C) and sulfide (175 M), ammonium (100 M), and H2 are plausible electron donors. However, electron acceptors other than sulfate (1.6 mM) are non detectable (NO3 −, NO2 −, Fe3+, Mn4+). Roughly 1/3 of the 16S rRNA fragments retrieved from the biofilm have no cultivated relatives at the order or phylum level. Data collected to date indicate that this system is likely to reveal new links between sulfate cycling and microbial lineages with no cultivated representatives.
Energy Produced from Serpentinization of Ultramafic Rocks on Terrestrial Planets: Implications for Sustaining Microbial Communities
Ultramafic rocks make up a major component of early terrestrial planetary lithospheres, forming from crystallization of mantle-derived melts or as cumulates from early magma oceans. On Earth, seawater and meteoric water react with the primary minerals in ultramafic rocks, olivine and pyroxene, to form serpentine, magnetite, brucite, and H2-rich fluids. Hydrogen released during serpentinization can act as an energy source for chemosynthetic organisms and therefore is of great importance to the emergence of life on Earth and elsewhere in the solar system. Additionally, H2 can combine with CO2 to produce abiotic methane and other organic compounds. The efficiency of these processes varies with temperature, pressure, and water/rock compositions, and on Earth, actively serpentinizing systems along the seafloor are capable of sustaining vast microbial biospheres.
In a series of water-rock reaction simulations using the program CHIM-XPT (after CHILLER, Reed 1998), we assess the process of serpentinization and quantify the amount of energy produced (kJ/mol) that could be available to sustain microbial communities. We begin by reproducing calculations for terrestrial seawater and meteoric water reacting with mantle harzburgite and then simulate reaction of terrestrial waters with martian meteorites representing ultramafic igneous (shergottite), cumulate (ALH 84001), and mantle (chassignite) compositions. Finally we calculate hypothetical waters in equilibrium with martian atmospheric CO2 and simulate reaction of these waters with martian rock compositions.
The recent discovery of evidence for crustal water, serpentine, and methane on Mars makes this work particularly timely, and will contribute to understanding the emergence of life in the Solar System.
Biogeography and Evolution of Microorganisms Associated with Mars-Analogue Serpentinites
Mars and Earth share a preponderance of ultramafic rocks. On Earth, terrestrial serpentinites host unique ecosystems where chemical energy is available in the form of hydrogen gas and methane. Organisms in these environments are adapted to extremely alkaline conditions and are geographically isolated from other comparable serpentinite systems. Our lab and collaborators are characterizing the microbiome and geochemistry of three such systems in an effort to understand the evolutionary mechanisms involved. We will compare genetic similarity between subsurface and surface organisms among and between sites to determine if the subsurface communities are more evolutionarily constrained than surface communities by environmental conditions and lack of recruitment. As we further describe these systems along with other serpentinite ecosystems we are locating and correlate the methane and other chemical signatures with the microbiology, insights will be gained that should prove useful when searching for suitable habitats on Mars.
My project is also concerned with the physiological adaptation to alkaline environments. Above pH 10, the proton gradient that normally powers ATP generation and various membrane motors becomes reversed. By studying these genes and proteins, I gain evolutionary insights as well as an understanding of alkaline ecology.
The Last Puddle on Earth: Finding the Final Habitable Regions on the Planet
The Sun, at an age of 4.57 Gyr, is approximately halfway through its main-sequence lifetime. As the Sun ages, its luminosity (and, thus, the solar radiation flux received on Earth) increases, leading to increased surface temperatures on Earth over geological time scales. Within the next 1–2 Gyr, surface temperatures will have risen sufficiently that the oceans will have evaporated, with the planet's water being lost to space via photodissociation of stratospheric water vapor.
The rate of temperature change on Earth will vary depending on location. Different locations will receive different levels of solar flux per unit area due to a combination of factors, including latitude and orbital characteristics such as eccentricity, obliquity and precession (all of which vary over geological timescales quantified by the Milankovitch Cycles). A “toy model” of the Earth's climate system is used to determine surface temperature increases caused by growing solar luminosity and, crucially, the likely location of the regions where liquid water can still remain on the surface. As liquid water is a prerequisite for life as we know it, these regions likely represent the last habitable refuges for life on Earth. Based on the expected environmental conditions, speculations are drawn about the nature of the last forms of life in the dying biosphere.
Laboratory Simulation of Interplanetary Charged Particle Radiation and Its Effects on Deinococcus radiodurans
In this experimental study cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate those charged particles found in the solar wind. Naked cells or cells mixed within dust grains (basalt or sandstone), themselves differing in elemental composition, were exposed to electrons, protons and ions to determine the probability of cell survival after irradiation. The doses necessary to reduce the viability of cell population to 10% (LD10) were determined under different experimental conditions. The results indicate that whilst low energy particle radiation (2 keV to 4 keV) has little or no effect on dehydrated cells, higher energy ions (200 keV) would inactivate the cells when a high flux is used (>1010 ions · cm−2). Considering the low flux of energetic particles originating from actual astrophysical sources, these results emphasize the resilience of life in space and provide support for the concept of an interplanetary transfer of viable microbes.
Relation Between Environmental Adaptability and Genetic Diversity of [FeFe]-Hydrogenases
Iron-sulfur clusters in proteins show some common features with iron-sulfur minerals and catalyze important reactions in the processes of metabolic energy transformations and carbon and nitrogen fixation. Enzymes harboring these clusters and enabling cells to use molecular hydrogen appeared during the earliest stages of life since hydrogen was the predominant component of the early Earth's atmosphere. By examining iron-sulfur enzymes as model systems to relate iron-sulfur clusters biosynthesis and iron-sulfur minerals, we are trying to characterize the transition between the early abiotic and biotic Earth. We have been studying [FeFe]-hydrogenases in order to understand the complexity of iron-sulfur clusters synthesis in biology and whether this biosynthetic pathway can be related to modifications on iron-sulfur minerals in the prebiotic Earth. The [FeFe]-hydrogenases are oxygen sensitive enzymes that catalyze reversible hydrogen oxidation and are involved in simple energy transformation in microorganisms. Some organisms, harboring fermentative metabolisms using hydrogenases, can compete in hostile oxygen-containing environments such as the phototrophic mats in Guerrero Negro. The use of degenerate primers to characterize the properties of the diversity of the hydrogenases found in Guerrero Negro will provide insights in how nature designed hydrogenases in such ecosystems and information about hydrogenase's evolution, their adaptability to their environment, but also information about the characteristics and the biosynthesis of the H-cluster, site of reversible hydrogen oxidation harboring a [4Fe-4S] cubane bridged to a 2Fe subcluster with unique non-protein ligands including carbon monoxide, cyanide, and a dithiolate.
A Closer Look at Asteroids
As people have realized how devastating effects massive asteroid impacts on Earth pose to the functioning of the civilization and, in the worst case, to the continued existence of human race, asteroid research has become one of the most important and well-funded areas of astronomy. Most of the funding lies in programs to detect the potentially hazardous asteroids, while most of the detailed tracking and scientific study of the asteroids is left to small projects and individual science teams. One such project is multinational EURONEAR, which observes recently detected Near Earth Objects (NEOs) in order to improve their calculated orbits and assess future motion and close encounters with Earth. Additionally the physical parameters of these objects, such as size, shape, albedo, and mineralogy, are estimated through careful analysis of their photometry, spectroscopy, and polarimetry.
The latest results of a EURONEAR survey of 558 known Main Belt Asteroids (MBAs) and 628 unknown moving objects, some of which are new discoveries, demonstrated the feasibility of 1–2 meter class telescopes in the study of Solar System asteroids and especially their value in quickly securing the orbits of new discoveries. Most unknown objects were found to be MBAs, but some 16 are suspected to be NEOs. New software was used to calculate orbital parameters of known and new objects, and was found to provide accurate orbits and good identification of the classification of objects under study.
Stabilization of Early Stage Nucleators in Calcium Phosphate Mineralization by α2-HS-Glycoprotein
By examining the events immediately before and after nucleation, the physicochemical effects of biomolecules on the nucleation of calcium phosphate (CP) minerals can be observed. Here, we investigate the effects on nucleation from bovine serum albumin (BSA), ovalbumin (OV), and α2-HS-glycoprotein (also known as Fetuin-A). We find that Fetuin-A delays significantly late stage nucleation events by way of stabilization of prenucleation as well as early stage nucleators of CP mineralization. This in effect shifts the equilibrium kinetics of CP mineralization and has severe ramifications on CP mineral morphologies. With the use of microanalytical in situ titration methods, we are able to observe the kinetics of CP mineralization with nM precision of Ca2+ in vitro. These studies provide an insight into the necessary chemical conditions required to probe the evolution of CP mineralization in biology.
Investigation of a Possible Solution to the Faint Young Sun Paradox: Elemental Sulfur Aerosols
In 1972, astronomers Carl Sagan and George Mullen presented the faint young Sun paradox, a discrepancy between the predicted subfreezing global surface temperature on the early Earth and geologic evidence of a warm planet. Standard models of solar evolution calculate that the Earth's surface temperature would have been below freezing until two billion years ago. However, geologic evidence indicates that surface liquid water existed long before that time. Past research on solutions to this problem has yielded inconclusive results. Atmospheric particles (aerosols) absorb radiation, and may therefore be a possible solution to the problem. Here, two separate investigations of the representation of particles in one-dimensional models are made. First, we validate treatment of particles in a photochemical model, using Saturn's largest moon, Titan. The results compare well with observations of Titan's albedo spectrum. Second, we attempt to solve the faint young Sun paradox with elemental sulfur particles. The optical properties for elemental sulfur particles are calculated using a Mie scattering code. They are then inserted into a one-dimensional photochemical model and a one-dimensional radiative-convective climate model, both configured for the Late Archean/Paleoproterozoic era on Earth (2.2 to 2.8 billion years ago). Inclusion of the sulfur particles in climate calculations lowers the surface temperature by 3 K. Despite the negative outcome, future investigations may yield more encouraging results. Perhaps other sulfur allotropes, such as S3 and S4, may help to counteract a faint young Sun.
Early Hydrogen Production on Carbonaceous Asteroids Could Support Subsurface Life
Subsurface life on Earth gains metabolic energy from geochemical substrates in the absence of light energy. Harsh conditions on the surfaces of asteroids predict that if life ever resided there, the subsurface may have been the most hospitable environment. While heat production and aqueous activity were previously estimated to be of a short (i.e., few My) for small asteroids, new modeling results suggest that larger bodies, such as Ceres, may have had more intense heating and a prolonged hydrological cycle, and may have been habitats for life for tens of My. However, the presence of liquid water alone is not enough to dictate habitable conditions; chemical energy sources are needed to sustain and perpetuate life. In carbonaceous asteroids, aqueous alteration of olivines and pyroxenes (i.e., serpentinization) results in H2 production when Fe is present. Microbial communities on Earth thrive near such serpentinizing systems, fueled by H2. Calculations suggest that under the physical conditions present in asteroids, constrained by CM meteorites, H2 production was significant. An additional source of H2 (and oxidants) is radiolytic splitting of H2O by abundant short-lived radionuclides (i.e., 26Al, 41Ca, 60Fe, 53Mn). The results from both serpentinization and radiolysis calculations will be presented in the context of energy sources available to support life should it have inhabited the subsurface of asteroids during their early, but short hydrological cycles.
The [Fe-Fe]-Hydrogenase: An Evolutionary Role of Conserved Domains
Many enzymes containing inorganic cofactors are thought to be responsible for processes essential to life, and they catalyze essential processes such as nitrogen fixation, carbon dioxide fixation, and hydrogen metabolism. These cofactors were possibly incorporated from mineral surfaces and yielded the enzymes that we presently observe. The [FeFe]-hydrogenase is an important example, as it is an enzyme that is essential for hydrogen metabolism, and it catalyzes the reversible reduction of protons. It is thought that this enzyme represents an ancient class of enzymes that evolved from FeS minerals due to their complex FeS cofactor that participates in catalysis. The conserved features of [FeFe]-hydrogenases can give valuable insight about their history and help determine the role conserved regions play. A fundamental principle to the idea of conservation of residues and/or structure is that these conserved features have an ancient origin that can be traced back to a common ancestor. Also they may be ancient and may have been what interacted with mineral surfaces removing chemical processes from mineral surfaces to cellular environments. Some of these enzymes may be able to be traced back to their metabolic origin because they catalyze reactions necessary for life, including but not limited to carbon dioxide reduction, nitrogen fixation, and proton reduction. Therefore, understanding the conserved domains of an enzyme like the [FeFe]-hydrogenase and how they interact with inorganic substrates may yield important insight into the understanding of how these possibly ancient domains may have interacted with mineral surfaces and why they have been maintained.
Extreme Autotrophic Bacteria on Earth Hold Potential for Microbiological Remediation of Martian Soil
Development of local agriculture will become crucial for permanent food and oxygen supplements for martian colonies. Recent studies show that martian soil may not be suitable for direct growth of plants due to high content of insoluble substances. Presence of damaging sulfates and possible hypochloride and peroxide could become overwhelming problem. Thus, bioremediation is the only option and could well be implemented with strains of extreme bacteria specifically chosen for their accelerated ability to metabolize mineral and chemical components presented in martian soil. Samples were collected from extreme environments: Iron bacteria, Silica bacteria, Sulfur Bacteria, Mycobacteria, Cyanobacteria, Actinomycetes, etc. Microbial species involved in remediation of manufacture and mine waste waters have been collected in light of their unique capability to clean extremely high contents of heavy metals. The samples were transferred onto imitated martian soil and stored. Further selection of microbes involved long-term storage in experimental chamber Mars with simulated planetary conditions. Thus, first microbial strains suitable for the bioremediation of martian soil have been obtained. Species of extreme Iron and Sulfur bacteria have been found to be able to trigger further processes for continuous bioremediation. Many species with nitrogen-fixing capabilities where found to be appropriate for second-step nutrition supplement growth of heterotrophic microbes such as Actinomycetes. Facultative anaerobes may function in presence or absence of oxygen. Surprisingly, presence of oxygen-release components, hydrogen peroxide or perchlorate, can supply oxygen for remediation in applications. Few species of methane bacteria, producing water, are also found to function with the presence of perchlorates.
Sulfolobus solfataricus: Mercury-Induced Stress Response
One of the most toxic substances on earth, yet one of the most scarce, is mercury, a leader in acute heavy metal poisoning. It occurs naturally in geological formations, usually in the form of cinnabar (HgS), and is released from the earth's crust into water bodies and into the atmosphere through geothermal features. Humanity's role in increasing surficial mercury has been ever more significant this past century and we now accounts for about two thirds of the total emissions. As we start to understand the problems associated with mercury in the environment, a better understanding of mercury's characteristics, both biotic and abiotic, is needed. Sulfolobus solfataricus possess a rare ability to cope with high levels of mercury, specifically Hg2+, which is also shared by a few bacterial strains. Studies of archaea are of interest for many reasons, including their extremophilia and subsequent protein stability that affords optimal functionality in extreme conditions such as high temperature. Here, we have characterized the growth of this thermoacidophilic archaea when exposed to different concentrations of mercuric chloride. We are employing a multi-pronged approach to examine the mercuric ion-induced stress response and subsequent mechanism of mercury reduction and volatilization that affords resistance to μM concentrations of mercury. This includes determining the concentration of mercury tolerated by S. solfataricus, proteomic analysis of mercury stressed cells, and heterologous expression of mercuric reductase (merA) for biochemical characterization and crystallization.
Unusual Gene Clusters in a B. pumilus Strain Producing Spores That Are Unusually Resistant to UV and Peroxide
Strains of Bacillus pumilus and B. licheniformis producing spores extremely resistant to UV and peroxide treatment have been isolated from spacecraft assembly facilities at the JPL, Caltech. Towards understanding the source of this resistance, the complete genomic sequence of the isolate, producing the most highly UV and peroxide resistant spores, B. pumilus SAFR-032, was compared with that of a non-resistant type strain B. pumilus ATCC7061. Amongst the most prominent contrasting features was the presence of twenty gene clusters (of at least three or more adjacent genes) in the genome of B. pumilus SAFR-032 not shared by the type strain B. pumilus ATCC7061. Several of these clusters were observed to have been flanked by phage integrase genes in the genome of B. pumilus SAFR-032. Detailed examination of the genes in the clusters reveal that, some of the genes in these clusters are unique (to the B. pumilus SAFR-032 genome), as well, besides being orthologous to genes either in other Bacillus species or even non-Bacillus species. We speculate that the persistent exposure to the high UV-radiation as well as peroxide, have both induced a selection pressure, leading to horizontal gene transfers mediated by integrases resulting in acquisition of genes by the B. pumilus SAFR-032. The results of the analysis of the gene clusters will be presented.
Abiotic Oxidation of Organic compounds in the Hyperarid Soils of La Joya Desert, Under Conditions of the Viking-Labeled Release Experiment: Implications for Possible Oxidants on Martian Soils
The Viking–Labeled Release (LR) experiment monitored the radioactive gas evolution after the addition of a 14C-labeled aqueous organic substrate into a sealed test cell that contained a martian surface sample. This experiment was designed to test martian surface samples for the presence of life by measuring metabolic activity and distinguishing it from physical or chemical activity. Interestingly, the interpretation of the Viking LR experiment was that the tested soils were chemically reactive and not biologically active, and that at least two oxidative processes with different kinetics were required to explain the observed decomposition of organics. In this work, we evaluated the decomposition of 13C-labeled organics added to 7 types of sample soils of the Pampas de La Joya, a recently new martian soil analogue, under the conditions of Viking LR experiment. Although, the results of this study showed that the mechanisms for the oxidation in these soils were different from the processes observed by the Viking, these soils showed high oxidant activity with nonbiological explanation. Interestingly, after a second injection of organics between the days 7 and 11, the soils showed a consistent biological oxidation. Importantly, the initial rapid CO2 release was not eliminated by heating in the LR experiment. Finally, the results with perchlorates and titanium dioxide modified by hydrogen peroxide, showed a similar kinetic behavior to that observed on martian soils.
Using Microbial Fuel Cell Technology to Detect Life in Desert Soil
Microbial fuel cells (MFCs) generate electrical power using metabolic redox reactions inside a modified electrolytic cell. In principle, this technology could also indicate whether metabolizing microorganisms are present in an environmental sample. An MFC was constructed to test this using soil samples collected near the Mars Desert Research Station (MDRS) in southeastern Utah. The anode and cathode chambers of the MFC each have volumes of 150 mL, contain eight graphite electrodes, and are separated by a proton-permeable membrane. During an experimental trial, soil samples are mixed with degassed, deionized water and placed in the anode chamber against a cathode containing aerated water. The voltage and current across the two chambers are measured over a period of four days, then the MFC is heat-sterilized and the control voltage is recorded for an additional two days.
During initial tests conducted at MDRS, the voltage measured from one soil sample was greater than that of its sterilized control, indicating that microbes were metabolizing during the experimental trial. Follow-up tests for three additional sample sites will be conducted, and each will be confirmed with live/dead fluorescent microscopy. If these follow-up tests are consistent with the initial results, they will indicate viability of an MFC to serve as a life-detection mechanism for both terrestrial and extraterrestrial environments—with the potential to detect non-carbon-based life utilizing redox chemistry for metabolic processes.
Searching for Genetic Factors Involved in Evolution of Bacillus subtilis to Enhanced Hypobaric Growth: Microarray Studies
Microbial life on Earth is capable of growing under wide extremes of temperature, salinity, or pH, and some deep-sea microorganisms (barophiles of peizophiles) are known to thrive at extreme high pressure. Low-pressure (hypobaric) environments are not represented on Earth, but the ability of organisms to survive under hypobaric conditions is highly relevant to the field of Astrobiology. In particular, evolution of microbial life on planets such as Mars would require growth under hypobaric conditions; terrestrial microbes capable of hypobaric growth could potentially become forward contaminants of landing sites during future Mars exploration missions. Results from previous experiments indicate that there exists a low-pressure barrier for the growth of many terrestrial bacteria of ∼25 mbar (by comparison, pressure at Earth's sea level is ∼1013 mbar, and the average pressure at the martian surface is ∼7 mbar). We propagated wild-type Bacillus subtilis strain WN624 for 1,000 generations at 50 mbar, a pressure at which it grows very poorly, and isolated a strain called WN1106 that showed increased growth at 50 mbar. We performed a series of transcription microarray comparisons of ancestral strain WN624 and low pressure-evolved strain WN106 in order to identify candidate genes that could possibly explain the increase in hypobaric growth of strain WN1106. Increased expression was observed in strain WN1106 of several candidate genes or operons that are known to be involved in: (i) the general stress response, (ii) anaerobic growth, and (iii) pressure response in peizophilic microorganisms. These candidate genes are currently being subjected to individual characterization.
Phyllosilicate Deposits in Shalbatana Vallis
Shalbatana Vallis is an ancient river valley on Mars, the westernmost of the southern Chryse outflow channels. The geologic history of this area has significant implications for understanding Mars' hydrologic and climate history. A number of CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) images with strong phyllosilicate signatures have been identified throughout the channel and nearby highlands. We contribute to the understanding of the geologic history of Shalbatana Vallis using data from the HiRISE (High Resolution Imaging Science Experiment) and CTX (Context) cameras and the CRISM spectrometer on the MRO (Mars Reconnaissance Orbiter) spacecraft, and evaluating the mineralogy, origin, and placement of Fe/Mg-rich and Al-rich phyllosilicates in the region. The study found Fe/Mg-rich phyllosilicates consistent with nontronites, distinctly layered and occurring at various altitudes, analogous to multiple phyllosilicate-rich interbeds within layers of flood basalts. There were fewer examples of Al-rich phyllosilicates, but the signatures within the basin of Orson Welles Crater are scattered and display no clear layering, the only selections within the study area favoring detrital phyllosilicates. Since such minerals can form by a variety of different geological processes, such as weathering, burial diagenesis, and hydrothermal alteration, the nature of the phyllosilicate deposits in the Shalbatana Vallis region may provide insights into the formation processes that took place and help to place constraints on the early aqueous activity in the region.
Mars Life Detection with Chiral Amino Acids
The Labeled Release (LR) experiment, one of the life detection experiments conducted on Mars during the Viking mission, was positive. Soil degraded amino acids and carbohydrates to carbon dioxide as if they contained microorganisms. However, no native soil organic carbon was detected by the Viking gas chromatograph mass spectrometer, suggesting that the LR detected an abiotic phenomenon. Possibly, martian soils do not contain microorganisms, but instead contain inorganic oxidants, photochemically produced by ultraviolet irradiation. A future mission could test these two alternative explanations by administering pure amino acid enantiomers to soils. Biological activity is expected to consume either L- or D-enantiomer, whereas chemical oxidation is expected to destroy both. We studied this idea in terrestrial soils by using alanine, glutamic acid, aspartic acid, and leucine. In all cases, the uptake and consumption of the L-enantiomer began immediately after it was added. In contrast, the utilization of its mirror image D-enantiomer did not begin until many hours later. All bacteria, and some fungi and some archaea, possess racemase enzymes for catalyzing conversion between L- and D-enantiomers. We suggest that exposure to D-amino acids triggered an increased production of these racemases, allowing soil microorganisms to grow on D-enantiomers. The results validated the utility of chiral amino acids in Mars life detection and revealed that this approach has limitations.
The Potential Role of Bacterial Extracellular Polymeric Substances (EPS) in Shielding Against Toxic Metal Surfaces
The bacterial cell surface is a complex system of phospholipid membranes, membrane proteins, peptidoglycan layers, lipopolysaccharides, and extracellular polymeric substances (EPS). The evolution of EPS is likely related to its many functions in promoting lateral gene transfer, quorum signaling, and protection from environmental extremes such as dessication, UV radiation, pH and temperature fluctuations, and dissolved toxic metals. Here, we propose a previously unrecognized role of EPS in protecting against the toxicity of certain mineral surfaces, a function that is distinct from the binding of soluble metals and precipitation of solid phases by EPS, and determine the specific toxicity mechanism of the minerals in terms of chemical composition, surface charge, surface-bound reactive oxygen species (ROS), and particle size. We report results for Gram-positive bacteria Bacillus subtilis wild type (3610) and its EPS-defect mutant (yhxBD) when exposed to model oxides, β-TiO2 (anatase) and γ-Al2O3. Preliminary results indicate that cells that have been gently washed in saline to remove all traces of EPS are more susceptible to oxide exposure compared to their oxide-free controls and their unwashed counterparts. We also compare our results to the response of Gram-negative bacteria, Pseudomonas aeruginosa wild type (PAO1) and EPS-deletion mutant (δ-psl), obtained previously in our laboratory.
AbGradCon 2011 Abstract Author Index
Adam, Zachary, AGC11-p01
Aponte, José C., AGC11-t01
Arney, Giada, AGC11-p02
Atri, Dimitra, AGC11-t02
Azúa-Bustos, Armando, AGC11-t03
Bauermeister, Anja, AGC11-t04
Beard, Trevor, AGC11-t05
Bernier, Chad R., AGC11-p03
Black, Paul, AGC11-t06
Booth, Mark, AGC11-t07
Boswell, Nicholas, AGC11-t08
Braswell, Shaneen, AGC11-p04
Chopra, Aditya, AGC11-t09
Cole, Callie, AGC11-t10
Craft, Kathleen L., AGC11-t11
DeMarines, Julia, AGC11-t12
Demarais, Nicholas, AGC11-p05
Diemer, Geoffrey, AGC11-t13
Domagal-Goldman, Shawn D., AGC11-t14
Dressing, Courtney, AGC11-p06
Duffus, Benjamin, AGC11-t15
Foster, Ian S., AGC11-t16
Fournier, Greg, AGC11-t17
Frank, Elizabeth, AGC11-p07
Gardenghi, David, AGC11-p08
Goldman, Aaron, AGC11-t18
Goldschmidt, Gergely, AGC11-p09
Goordial, Jacqueline, AGC11-t19
Gordon, Alexander, AGC11-p10
Greiner, Edward, AGC11-p11
Guaman, Christian, AGC11-p12
Hamilton, Trinity, AGC11-t20
Jarrett, Amber J.M., AGC11-p13
Johnson, Savannah J., AGC11-t21
Joshi, Neelambari, AGC11-p14
Kazmierczak, Maja, AGC11-p15
Knowles, Emily, AGC11-p16
Konesky, Gregory, AGC11-t22
Lamarche-Gagnon, Guillaume, AGC11-p17
Longo, Riccardo, AGC11-t23
Lynch, Kennda, AGC11-t24
Mackey, Tyler, AGC11-p18
Marcucci, Emma, AGC11-p19
Marnocha, Cassandra, AGC11-p20
McCauley, Rebecca, AGC11-p21
Mercer, Celestine N., AGC11-p22
Moazeni, Faegheh, AGC11-t25
Morschhauser, Achim, AGC11-t26
Nelson, Bridget, AGC11-p23
Noell, Aaron, AGC11-t27
O'Malley-James, Jack, AGC11-p24
Paulino-Lima, Ivan Gláucio, AGC11-p25
Pienton, Cedric, AGC11-p26
Rekola, Rami, AGC11-p27
Robinson, Tyler, AGC11-t28
Schmidt, Britney, AGC11-t29
Schröder, Susanne, AGC11-t30
Seto, Jong, AGC11-p28
Siemion, Andrew, AGC11-t31
Smith, Megan, AGC11-p29
Spivak-Birndorf, Lev, AGC11-t32
Swanner, Elizabeth, AGC11-p30
Swanson, Kevin, AGC11-p31
Tarasashvili, Mariam, AGC11-p32
Therien, Jesse, AGC11-p33
Tirumalai, Madhan, AGC11-p34
Valdivia-Silva, Julio, AGC11-p35
Viola, Donna, AGC11-p36
Vixie, Graham, AGC11-t33
Walker, Sara Imari, AGC11-t34
Waters, Samantha, AGC11-p37
Williams, Amy, AGC11-t35
Wintzer, Anne, AGC11-p38
Wolf, Eric, AGC11-t36
Wright, Katherine E., AGC11-t14
Zhang, Gaosen, AGC11-p39
Zhu, Chunxiao, AGC11-p40
Footnotes
Oral abstracts can be found on pp. 368–377; Poster abstracts on pp. 378–388.