Enhancement of bacterial rheotaxis in non-Newtonian fluids

TL;DR

This study reveals that bacteria exhibit significantly enhanced upstream swimming in shear-thinning non-Newtonian fluids, driven by flow-induced torque, with a developed model accurately describing this behavior.

Contribution

It introduces the first experimental and theoretical analysis of bacterial rheotaxis in non-Newtonian fluids, highlighting the impact of shear-thinning properties on bacterial upstream swimming.

Findings

Upstream swimming is enhanced by an order of magnitude in shear-thinning fluids.

A torque promotes bacterial alignment against flow in non-Newtonian fluids.

A theoretical model accurately predicts rheotactic behavior in both Newtonian and shear-thinning fluids.

Abstract

Bacteria often exhibit upstream swimming, which can cause the contamination of biomedical devices and the infection of organs including the urethra or lungs. This process, called rheotaxis, has been studied extensively in Newtonian fluids. However, most microorganisms thrive in non-Newtonian fluids that contain suspended polymers such as mucus and biofilms. Here, we investigate the rheotatic behavior of E. coli near walls in non-Newtonian fluids. Our experiments demonstrate that bacterial upstream swimming is enhanced by an order of magnitude in shear-thinning polymeric fluids relative to Newtonian fluids. This result is explained by direct numerical simulations, revealing a torque that promotes the alignment of bacteria against the flow. From this analysis, we develop a theoretical model that accurately describes experimental rheotatic data in both Newtonian and shear-thinning fluids.