The identity of the pigments in the purple bacteria

There exist certain groups of bacteria which possess a peculiar purple color. This color ranges from a pale bluish pink to a deep crimson, almost like Ruthenium red. The bacteria concerned may be grouped according to their physiological behavior into four distinct classes:

The almost algal Chromatium, the pediococcoid Thiopedia, Spirillæ, Bacillæ, and Cocci all possess the pigment purple color.

There is therefore no a priori evidence for the identity of the pigments.

Classes I and II, the true Rhodobacteria, seem to have identical pigments (Molisch). One of them is red, probably a carotinoid, bacterio-erythrin, the other is green, soluble in absolute alcohol and is called bacteriochlorin∗. The combination of both pigments is called bacteriopurpurin. Bacteriochlorin has a marked narrow absorption-band with an axis near the sodium lines D.

Bacterio-erythrin is characterized by two distinct absorption bands in the green and bluegreen.

An absolute alcohol extract of Thiopolycoccus yielded a green solution with a bluish green fluorescence. The fluorescence spectrum of this solution will be discussed elsewhere.

The spectra of the following forms were studied.

a. Thiopolycoccus, from a brackish, arsenic-containing, black mud from Owen's lake, California (collected spring 1924 by Dr. F. M. Scott), raspberry color.