Effective run-and-tumble dynamics of bacteria baths

TL;DR

This paper investigates the collective dynamics of bacteria in dense baths, demonstrating that a simplified run-and-tumble model with effective parameters can accurately describe density fluctuations at high concentrations.

Contribution

It introduces a method to model dense bacterial baths using an effective run-and-tumble framework, extending beyond the dilute limit.

Findings

Density fluctuations can be modeled with an effective run-and-tumble approach.

Model parameters depend on bacterial density.

Simulations match experimental-like density fluctuation data.

Abstract

{\it E. coli} bacteria swim in straight runs interrupted by sudden reorientation events called tumbles. The resulting random walks give rise to density fluctuations that can be derived analytically in the limit of non interacting particles or equivalently of very low concentrations. However, in situations of practical interest, the concentration of bacteria is always large enough to make interactions an important factor. Using molecular dynamics simulations, we study the dynamic structure factor of a model bacterial bath for increasing values of densities. We show that it is possible to reproduce the dynamics of density fluctuations in the system using a free run-and-tumble model with effective fitting parameters. We discuss the dependence of these parameters, e.g., the tumbling rate, tumbling time and self-propulsion velocity, on the density of the bath.