Q-293. Aggregation of Clay-Bacteria-Exopolysaccharide (EPS) in Electrohydrodynamically-Defined Suspensions of Shewanella spp

J. R. Dale, Y. Furukawa;
Naval Res. Lab., Stennis Space Center, MS.

Particle electrokinetic properties affect the aggregation of clay-bacterial cell-EPS. Aggregation processes in natural waters, however, are poorly understood. Electrophoretic mobility and cell aggregate size in aqueous suspensions containing S. putrefaciens strain 200 cells, S. oneidensis strain MR-1 cells or the EPS isolated from aerobically-or anaerobically-grown Shewanella cultures was determined over a range of environmental parameters (i.e., 4 ~ pH ~ 10; [KCl] ~ 100 mM) via Laser Doppler Velocimetry and Dynamic Light Scattering to test the hypothesis that growth status and physiochemical conditions control cell aggregation. S. oneidensis formed stable colloidal suspensions over the entire range of pH and [KCl] regardless of the terminal electron acceptor. S. putrefaciens, on the other hand, formed 3-6 μm aggregates at 5 ~ pH ~ 7.5 and at [KCl] < 50 mM despite its high electronegativity at these pH and [KCl]. Cell aggregation of S. putrefaciens was concurrent with the aggregation of EPS isolated from S. putrefaciens culture supernatant. EPS was copiously produced by S. putrefaciens under anaerobic conditions and aggregated rapidly at pH < 7 and [KCl] < 50 mM. EPS aggregates behaved as amphoteric particles when suspended in distilled water, whereas the specific adsorption of electrolytes in solutions with high KCl concentrations (i.e., [KCl] > 60 mM) caused them to behave as electroneutral, hydrophobic particles, although the kinetically slow protonation and deprotonation processes inferred from the drifting pH during potentiometric titration suggests their electrophoretic softness. These results indicate that the aggregation of bacterially-produced exopolymers influence estuarine aggregation processes over a wide range of pH and salinity.