Effect of Topographical Steps on the Surface Motility of the Bacterium Pseudomonas aeruginosa

Bacteria traverse surfaces as part of colonizing solids, and it is of interest to hinder this motion to potentially thwart infections in humans. Here, we demonstrate that topographical steps hinder the ability of Pseudomonas aeruginosa PAO1 (P. aeruginosa) to traverse a solid-liquid interface. Using time-lapse fluorescence microscopy and image analysis, we analyzed the motion of P. aeruginosa that were challenged with steps ranging in height from 0.4 to 9.0 pm. Bacterial trajectories are sensitive to the height of the step, the curvature of the step face, and the direction of their motion relative to gravity. When the step height is >= 0.9 mu m, which is similar to the cell diameter, there is a reduced probability of the cell crossing the step. For those bacteria that do cross a step, there is a time penalty for crossing steps of height 2-3 mu m; this height is similar to the length of the bacterium. For higher steps, the bacteria reorient their cell body while traversing the step riser. Our findings elucidate how topography influences the motion of bacteria and informs strategies for hindering bacterial motion at surfaces.