ANALYSIS OF BACTERIAL SWIMMING SPEED APPROACHING A SOLID-LIQUID INTERFACE

Previous experimental studies have found that surface interactions sig nificantly affect the transport of motile bacteria through small tubes , along solid surfaces, and through porous media. However, the role th at hydrodynamic forces play in the interactions between solid surfaces and motile bacteria remains unclear. In this study, the swimming spee ds of populations of Escherichia coli bacteria were measured near (<10 mu m) and far (>10 mu m) from a flat glass surface at four ranges of orientations to the surface (0 degrees-45 degrees 45 degrees-90 degree s, 90 degrees-135 degrees and 135 degrees-180 degrees). Populations of bacteria close to the surface and moving in the orientation range mos t perpendicular (0-45 degrees) to the surface experienced the greatest change in the swimming speed when compared to the population in the s ame orientation range located far from the surface. The decrease in sw imming speed experienced by this population was on the same order as t hat predicted by hydrodynamic models of bacterial swimming near surfac es.