High shear flow prevents bundling of bacterial flagella and induces lateral migration away from a wall

Abstract

Since the discovery of bacteria in the 17th century, bacterial motion has been the focus of great research interest. As an example of bacterial chemotaxis, Escherichia coli exhibits run-and-tumble motion by bundling and unbundling flagella, propelling the cells along a concentration gradient. However, the behavior of bacteria in high-shear flow environments remains poorly understood. In this study, we showed experimentally that E. coli swimming is severely inhibited at shear rates above a few hundred per second. Our simulations revealed that E. coli flagellar bundling cannot occur in a high-shear regime, because the background shear flow is stronger than the flagellar-generated flow required to form a bundle. Bacteria under strong shear behave like deformable objects and exhibit lateral migration away from a wall. These results suggest that bacteria that are unable to bundle their flagella in strong shear near a wall alter their locomotion strategy to passively escape from the wall.