Oscillatory surface rheotaxis of swimming E. coli bacteria

TL;DR

This study investigates how E. coli bacteria reorient and swim against flow in complex environments, revealing oscillatory behaviors and multiple transition thresholds through experiments and modeling, which enhance understanding of bacterial transport and contamination control.

Contribution

The paper introduces a combined experimental and theoretical analysis of bacterial rheotaxis, discovering oscillatory behavior and multiple flow-dependent transitions in E. coli swimming dynamics.

Findings

Identification of three shear rate thresholds for bacterial reorientation.

Discovery of oscillatory rheotaxis at intermediate shear rates.

Theoretical model accurately predicts experimental transition points.

Abstract

Bacterial contamination of biological conducts, catheters or water resources is a major threat to public health and can be amplified by the ability of bacteria to swim upstream. The mechanisms of this rheotaxis, the reorientation with respect to flow gradients, often in complex and confined environments, are still poorly understood. Here, we follow individual E. coli bacteria swimming at surfaces under shear flow with two complementary experimental assays, based on 3D Lagrangian tracking and fluorescent flagellar labelling and we develop a theoretical model for their rheotactic motion. Three transitions are identified with increasing shear rate: Above a first critical shear rate, bacteria shift to swimming upstream. After a second threshold, we report the discovery of an oscillatory rheotaxis. Beyond a third transition, we further observe coexistence of rheotaxis along the positive and negative vorticity directions. A full theoretical analysis explains these regimes and predicts the corresponding critical shear rates. The predicted transitions as well as the oscillation dynamics are in good agreement with experimental observations. Our results shed new light on bacterial transport and reveal new strategies for contamination prevention.