Hydrodynamic attraction of swimming microorganisms by surfaces

TL;DR

This study investigates how swimming bacteria are attracted to surfaces, combining experimental measurements with a hydrodynamic model to explain their distribution and estimate propulsive forces.

Contribution

It provides a theoretical model linking hydrodynamic interactions to bacterial surface attraction and validates it with experimental data, also estimating bacterial propulsive force.

Findings

Bacteria accumulate near surfaces due to hydrodynamic interactions.

The model accurately predicts the steady-state distribution of bacteria.

Estimated flagellar propulsive force in E. coli from data.

Abstract

Cells swimming in confined environments are attracted by surfaces. We measure the steady-state distribution of smooth-swimming bacteria (Escherichia coli) between two glass plates. In agreement with earlier studies, we find a strong increase of the cell concentration at the boundaries. We demonstrate theoretically that hydrodynamic interactions of the swimming cells with solid surfaces lead to their re-orientation in the direction parallel to the surfaces, as well as their attraction by the closest wall. A model is derived for the steady-state distribution of swimming cells, which compares favorably with our measurements. We exploit our data to estimate the flagellar propulsive force in swimming E. coli.