Negative bacterial chemotaxis induced by surface interaction

Bacterial chemotaxis is the ability of cells to bias their movement in response to chemical signals. Among the species of chemotactic bacteria, E. coli is the most studied and its strategy is now well documented. When free swimming in a quiescent fluid, E. coli cells move in quasi-rectilinear trajectories (runs), interrupted by quick reorientations (tumbles). In response to certain amino acids, the length of the bacterial runs are biased and, as a result, the cell effectively drifts towards high concentration regions of chemoattractant. Although it is an efficient search strategy in quiescent fluids, chemotaxis can be disrupted in a shear flow due to an induced rotation of the cell body. Swimming bacteria are often found in confined environments, and hydrodynamic interactions with surfaces may hinder chemotaxis in a similar fashion as shear flow does. In this study we explore theoretically the effects of near-surface swimming on E. coli chemotaxis in the small gradient regime. We show in particular that negative chemotaxis can be induced by a change in the curvature of the cell trajectories.