A shear-induced limit on bacterial surface adhesion in fluid flow

TL;DR

This paper develops a theoretical model to understand how fluid flow and bacterial motility influence bacterial adhesion to surfaces, revealing a shear-induced limit that maximizes adhesion at intermediate flow rates.

Contribution

The study introduces a hybrid asymptotic-computational approach to derive bacterial diffusivity near surfaces and establishes an analytical upper bound for adhesion rates considering shear effects.

Findings

Maximal bacterial adhesion occurs at intermediate flow rates.

Increasing flow initially increases adhesion, then decreases it at higher shear.

Shear-induced reorientation reduces adhesion at high flow rates.

Abstract

Controlling bacterial surface adhesion and subsequent biofilm formation in fluid systems is crucial for the safety and efficacy of medical and industrial processes. Here, we theoretically examine the transport of bacteria close to surfaces, isolating how the key processes of bacterial motility and fluid flow interact and alter surface adhesion. We exploit the disparity between the fluid velocity and the swimming velocity of common motile bacteria and, using a hybrid asymptotic-computational approach, we systematically derive the coarse-grained bacterial diffusivity close to surfaces as a function of swimming speed, rotational diffusivity, and shape. We calculate an analytical upper bound for the bacterial adhesion rate by considering the scenario in which bacteria adhere irreversibly to the surface on first contact. Our theory predicts that maximal adhesion occurs at intermediate flow rates: at low flow rates, increasing flow increases surface adhesion, while at higher flow rates, adhesion is decreased by shear-induced cell reorientation.