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

The data in this paper are all available. Data both in main text and SM are stored as the Data set.zip file. Data points used in figures are stored in csv format. The first row of each file contains the names of corresponding columns. Contact information: Minjun Kim([e-mail]) Joonwoo Jeong ([e-mail]) 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 reaction-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.