The role of tumbling in bacterial scattering at convex obstacles

TL;DR

This study investigates how bacterial tumbles influence their scattering behavior at microfluidic obstacles, revealing their impact on diffusivity and interactions in porous environments.

Contribution

It provides experimental insights into the role of tumbles in bacterial scattering at obstacles, comparing wild-type and smooth-swimming mutants.

Findings

Tumbles affect scattering angles and trajectories.

Tumble behavior influences bacterial diffusivity.

Experimental results support models predicting enhanced diffusivity due to tumbling.

Abstract

Active propulsion, as performed by bacteria and Janus particles, in combination with hydrodynamic interaction results in the accumulation of bacteria at a flat wall. However, in microfluidic devices with cylindrical pillars of sufficiently small radius, self-propelled particles can slide along and scatter off the surface of a pillar, without becoming trapped over long times. This non-equilibrium scattering process has been predicted to result in large diffusivities, even at high obstacle density, unlike particles that undergo classical specular reflection. Here, we test this prediction by experimentally studying the non-equilibrium scattering of pusher-like swimmers in microfluidic obstacle lattices. To explore the role of tumbles in the scattering process, we microscopically tracked wild-type (run and tumble) and smooth-swimming (run only) mutants of the bacterium Escherichia coli scattering off microfluidic pillars. We quantified key scattering parameters and related them to previously proposed models that included a prediction for the diffusivity, discussing their relevance. Finally, we discuss potential interpretations of the role of tumbles in the scattering process and connect our work to the broader study of swimmers in porous media.