Collective dynamics of bacteria in self-made oxygen gradients

In biological and environmental scenarios, such as mucus in the lungs and subsurface porous media, bacterial colonies experience strong confinement in tight spaces with varying spatial oxygen availability. This leads to the question of how such oxygen fluctuations influence the collective behavior of motile bacteria. In this study, we investigate this phenomenon experimentally by observing bacterial suspensions in micro-confinement, where self-generated oxygen gradients play a crucial role. Our findings demonstrate that the coupling between cellular motility and local oxygen concentration gives rise to the formation of two distinct phases: an immotile phase coexisting with a highly motile phase, reminiscent of Motility-Induced Phase Separation (MIPS). Additionally, we reveal how the active turbulence generated by the motile phase leads to fluctuations at the oxic-anoxic interface between the two phases, promoting an influx of oxygen and facilitating the propagation of this interface. Finally, we show how these collective dynamics are qualitatively different in a complex fluid akin to airway mucus. Our study uncovers the fascinating and diverse collective behaviors that emerge within bacterial populations when exposed to environments with physicochemical complexity.