Transition to bound states for bacteria swimming near surfaces

TL;DR

This paper investigates how certain bacteria transition from swimming in circles near surfaces to a surface-bound state, revealing a fluid-structure interaction instability that causes this behavior.

Contribution

It introduces a theoretical and simulation-based explanation for bacteria surface binding, highlighting a fluid-structure interaction instability as the underlying mechanism.

Findings

Bacteria can transition from swimming to surface-bound states.

Shorter flagella are more prone to surface binding due to instability.

The study combines numerical simulations with theoretical analysis.

Abstract

It is well known that flagellated bacteria swim in circles near surfaces. However, recent experiments have shown that a sulfide-oxidizing bacterium named Thiovulum majus can transition from swimming in circles to a surface bound state where it stops swimming while remaining free to move laterally along the surface. In this bound state, the cell rotates perpendicular to the surface with its flagella pointing away from it. Using numerical simulations and theoretical analysis, we demonstrate the existence of a fluid-structure interaction instability that causes cells with relatively short flagella to become surface bound.