Guided run-and-tumble active particles: wall accumulation and preferential deposition

TL;DR

This paper develops analytical models and simulations to understand how active bacteria like E. coli accumulate and deposit near surfaces, revealing the role of guiding fields and rotational drift in biofilm formation.

Contribution

The study provides the first analytical expressions for orientation, density, and deposition rates of active particles with external guiding fields, validated by simulations.

Findings

Guiding fields do not affect the size distribution of deposits.

Deposited structures' pair correlation functions become more spread out with guiding fields.

Asymmetrical rotational drift drives accumulation patterns and biomass architecture.

Abstract

Bacterial biofilms cost an enormous amount of resources in the health, medical, and industrial sectors. To understand early biofilm formation, beginning from planktonic states of active bacterial suspensions (such as Escherichia coli) to microcolonization, it is vital to study the mechanics of accumulation near surfaces and subsequent deposition. In this study, analytical expressions for the mean orientation, density and angular distributions, and deposition rates in such bacterial suspensions are derived, with and without the effects of external guiding or taxis fields. Simulations of confined active particles, using the run-and-tumble statistics from well-established three-dimensional tracking experiments and a preferential sticking probability model for deposition, closely verify the derived mean orientation, density profiles, angular distributions, and deposition rates. It is found that the size distribution of deposited microcolonies remains unaffected when guiding fields are applied, however, the pair correlation function of deposited structures relatively spreads out. The factor behind the changes in the accumulation patterns, and the changes in the architecture of deposited biomass, turns out to be an asymmetrical rotational drift caused by the guiding fields, and is an important physical mechanism behind the organization in confined active particle suspensions.