Density-Dependent Transition in Bacterial Self-Organization Driven by Confinement and Aerotaxis

TL;DR

This study explores how bacterial density influences their spatial distribution in confined environments, revealing a transition from wall accumulation to aerotactic migration driven by self-generated oxygen gradients.

Contribution

The paper introduces a diffusion-advection model that captures the density-dependent transition in bacterial self-organization driven by confinement and aerotaxis.

Findings

At low densities, bacteria accumulate symmetrically at both walls.

Higher densities induce migration toward the oxygen source due to self-generated gradients.

The model quantitatively matches experimental bacterial distribution patterns.

Abstract

We experimentally investigate how aerotactic bacteria, confined within a thin liquid film between two solid substrates, respond to a controlled oxygen gradient. We find that the total bacterial number density dictates which mechanism dominates the steady-state spatial distribution: wall accumulation or aerotaxis. At low densities, despite receiving oxygen only from one substrate, motile bacteria accumulate at both walls, forming a symmetric distribution. In contrast, pronounced aerotactic migration toward the oxygen-supplying wall emerges as the density increases. Analyzing the temporal evolution of this bacterial distribution reveals that the aerotactic response is driven by a self-generated oxygen gradient induced by collective respiration. Our diffusion-advection model of bacteria and oxygen, accounting for aerotactic migration, hydrodynamic attraction to the walls, and respiration, quantitatively reproduces our experimental observations and provides valuable insights into bacterial self-organization within complex environments.