Idling Time of Swimming Bacteria near Particulate Surfaces Contributes to Apparent Adsorption Coefficients at the Macroscopic Scale under Static Conditions

2009-12-01T00:00:00Z (GMT) by Jun Liu Roseanne M. Ford
Static capillary assays were performed to observe the distribution of <i>Escherichia coli</i> and several mutant strains at the interface between an aqueous solution and a Gelrite particulate suspension, used as a model porous medium. Motile smooth-swimming mutant bacteria (<i>E. coli</i> HCB437) accumulated at the interface, but did not penetrate very far into the Gelrite suspension. Motile wild-type bacteria (<i>E. coli</i> HCB1) penetrated much further than the smooth-swimming mutant, but did not accumulate to the same extent at the interface. Nonmotile tumbly mutant bacteria (<i>E. coli</i> HCB359) did not accumulate or penetrate to a significant degree. Computer simulations using a Monte Carlo algorithm, with input parameters based on bacterial swimming properties in static bulk aqueous systems, appeared to underestimate the bacterial idling time associated with solid surfaces. To account for physicochemical, biological and geometrical influences, an additional component of the bacterial idling time was included. The third component of the idling time was further analyzed semiquantitatively with a 1-D population-scale transport model with first-order association (<i>k</i><sub>on</sub>) and dissociation (<i>k</i><sub>off</sub>) adsorption-like kinetics. Computer simulation results suggested that this additional bacterial idling time not only increased the magnitudes of <i>k</i><sub>on</sub> and <i>k</i><sub>off</sub>, but also enhanced the ratio of <i>k</i><sub>on</sub> to <i>k</i><sub>off</sub>. This further implies that motile bacteria may tend to accumulate at the boundaries of low-permeable regions in groundwater systems, which is beneficial for bioremediation of residual contamination that may not be accessible by conventional remediation approaches.