History-dependent attachment ofPseudomonas aeruginosato solid-liquid interfaces and the dependence of the bacterial surface density on the residence time distribution.

This study investigates how the recent history of bacteria affects their attachment to a solid-liquid interface. We compare the attachment from a flowing suspension of the bacterium,Pseudomonas aeruginosaPAO1, after one of two histories: (a) passage through a tube packed with glass beads or (b) passage through an empty tube. The glass beads were designed to increase the rate of bacterial interactions with solid-liquid surfaces prior to observation in a flow cell. Analysis of time-lapse microscopy of the bacteria in the flow cells shows that the residence time distribution and surface density of bacteria differ for these two histories. In particular, bacteria exiting the bead-filled tube, in contrast to those bacteria exiting the empty tube, are less likely to attach to the subsequent flow cell window and begin surface growth. In contrast, when we compared two histories defined by different lengths of tubing, there was no difference in either the mean residence time or the surface density. In order to provide a framework for understanding these results, we present a phenomenological model in which the rate of bacterial surface density growth,dN(t)/dt, depends on two terms. One term models the initial attachment of bacteria to a surface, and is proportional to the nonprocessive cumulative residence time distribution for bacteria that attach and detach from the surface without cell division. The second term for the rate is proportional to the bacterial surface density and models surface cell division. The model is in surprisingly good agreement with the data even though the surface growth process is a complex interplay between attachment/detachment at the solid-liquid interface and cell division on the surface.