| In this study, we investigate the interaction between motile and nonmotile bacteria and surfaces in a system under flow. We developed a simple experimental procedure to measure the attachment and detachment rates of bacteria to a glass surface, to better understand how the swimming behavior of motile bacteria (both the presence and rotation of flagella) influenced adhesion in a dynamic system. Experiments were performed with wild-type, smooth-swimming, tumbly, paralyzed, and nonflagellate E. coli strains, for several fluid velocities and ionic strength solutions. We found that the transport of motile bacteria to surfaces by diffusion was similar in magnitude to the settling rate of nonmotile cells at low fluid velocities. At higher fluid velocities, motile bacteria attached at a faster rate than nonmotile bacteria. Motility also enhanced adhesion in a lower ionic strength medium, regardless of fluid velocities tested. We also observed that the combination of clockwise and counterclockwise flagellar rotation and their coupling appeared to be important in cell attachment.; We then related attachment rates measured in the flow chamber to porous media systems, so that we could predict cell transport and adhesion in a more complex, larger scale system. To calculate the attachment rate in porous media, it was necessary to determine first-order adsorption rate constants from measured flow chamber attachment rates using a mathematical model (via both an analytical solution and through numerical simulation). We showed that simple measurements in the flow chamber could be used to predict attachment behavior in a packed column, for similar materials and conditions.; Finally, we used a mathematical model to determine the conditions under which chemotaxis affected the attachment of bacteria to a pore surface. For typical pore dimensions and fluid conditions, we predicted an attractant gradient would be maintained at all times within a pore in the presence of fluid flow. The chemotactic velocities determined from these attractant profiles were on the same order of magnitude as typical groundwater flow rates, and increased the attachment rate by increasing the number of cells near the surface. Thus chemotaxis would be an important survival mechanism for bacteria in the environment and could lead to enhanced removal of chemical pollutants partitioned into the soil particles. (Abstract shortened by UMI.)... |
