Bacteria display optimal transport near surfaces

Abstract

The near-surface swimming patterns of bacteria are determined by hydrodynamic interactions between the bacteria and the surface, which trap the bacteria in smooth circular trajectories that lead to inefficient surface exploration. Here, we combine experiments with a data-driven mathematical model to show that the surface exploration of a pathogenic strain of Escherichia coli results from a complex interplay between motility and transient surface adhesion events. These events allow the bacteria to break the smooth circular trajectories and regulate their transport properties by exploiting stop events that are facilitated by surface adhesion and lead to characteristic intermittent motion on surfaces. We find that the experimentally measured frequency of these stop-adhesion events coincides with the value that maximizes bacterial surface diffusivity according to our mathematical model. We discuss the applicability of our experimental and theoretical results to other bacterial strains on different surfaces. Our findings suggest that swimming bacteria use transient adhesion as a generic mechanism to regulate surface motion. Bacteria swimming near surfaces can get trapped in circular trajectories that lead nowhere, hindering efficient surface exploration. A harmful strain of bacteria is now shown to circumvent the problem by exploiting transient surface adhesion events.