Bacterial swimming motility enhances cell deposition and surface coverage

The influence of bacterial motility on cell transport and deposition was investigated in a well-characterized radial stagnation point flow (RSPF) chamber. Deposition experiments were conducted with nonmotile (PAO1 Delta fliC Delta pilA) and motile (PAO1 Delta pilA) strains of Pseudomonas aeruginosa, and oppositely (positively) charged modified quartz surfaces. Deposition dynamics of the two bacterial strains were determined over a wide range of solution ionic strengths and at two flow velocities. The observed deposition dynamics were modeled using a modified expression of the random sequential adsorption (RSA) blocking function accounting for the impacts of hydrodynamic and electrostatic interactions on cell deposition. Results for the nonmotile bacteria indicated that the changes in blocking rate and surface coverage with ionic strength and flow rate were similar to those expected for nonbiological, "soft" particles, for which the coupling of hydrodynamic interactions and electrostatic repulsion governs the deposition dynamics. In contrast, deposition dynamics of the motile bacterial cells reduced blocking rates and enhanced maximum coverages, approaching the jamming limit predicted for "hard" ellipsoids of 0.583. We hypothesized that cell motility allows the upstream swimming of bacteria and subsequent cell deposition on regions which are otherwise inaccessible to nonmotile cell deposition due to the "shadow effect".