Surfactant effect on collective dynamics of surface-associated bacterial particles

Bacteria exhibit collective behavior on moist agar surface to expand and acquire new territories. Self-produced surfactant could entail a significant surface activity due to the reduction of the interfacial friction between moving bacteria and substrates. The bacteria density determines surfactant concentration, so that surface motility will vary locally. The contribution of the density-dependent motility to the collective behavior of bacteria communities remains unclear. We use a discrete self-propelled particle model to simulate an ensemble of rod-like bacteria without the background fluids. The self-propulsion speed is coupled with the local surfactant concentration, solved by a diffusion equation that describes the surfactant production and transport. Simulations between constant self-propulsion speeds will serve as the comparison to test the influence of surfactant. Our investigation will provide a deep understanding of how surfactant influence the collective behavior of bacteria, and further inspire new designs of active materials.