Adhesion of Pseudomonas putida KT2442 Is Mediated by Surface Polymers at the Nano- and Microscale

Pseudomonas putida KT2442 is a bacterium with potential for use in bioremediation of chlorinated hydrocarbons in soils, and its behavior in the subsurface is believed to be controlled by surface polymers. The role of surface macromolecules on the retention and adhesion behavior of this bacterium was examined by bacterial treatment with cellulase, an enzyme that breaks down the β(1 → 4) linkages of cellulose and similar macromolecules. Enzymatic treatment involved centrifugation to separate bacteria from suspending media. Two types of control systems were evaluated, namely, cells separated from growth media via filtration and centrifugation. Bacterial retention was quantified by the collision efficiency, α, the fraction of collisions that result in attachment. In batch retention studies (to glass), both controls had the same α values (1.19 ± 0.25, 1.20 ± 0.23, for filtered and centrifuged cells, respectively). In column transport/retention assays (to quartz), αs for the control groups were not statistically different from one another (0.34 ± 0.06, 0.45 ± 0.07, for filtered and centrifuged cells, respectively; data fails Mann-Whitney Rank Sum test). Treatment with cellulase decreased cell retention in both systems. The α values were decreased by 40% for cellulase-treated cells in batch tests, to 0.69 ± 0.13, and in column tests, cells treated with cellulase had α values below those from either control group (0.21 ± 0.05). Retention was correlated with nanoscopic adhesion forces measured with an atomic force microscope (AFM), as treatment with cellulase decreased adhesion forces from 1.05 ± 0.07 to 0.51 ± 0.03 nN. These results suggest that surface modification of P. putida KT2442 with cellulase alters adhesion/retention properties at the batch, column, and nanoscale, due to removal of polysaccharide material.