Catch your breath: time-dependent bacterial turbulence in the presence of oxygen diffusion

The swimming of the bacterium Escherichia coli is powered by the local availability of dissolved oxygen in water. Swimming bacteria in a dense suspension drive fluid flows giving rise to jet and vortex-like patterns termed “bacterial turbulence.” Here, we use confocal microscopy to image the bacterial turbulent flow in a cylindrical well where the top surface is in contact with ambient air. We find that the interplay between the molecular diffusion of oxygen, the consumption of oxygen by the swimming bacteria, and the self-generated advective flows results in an unexpected time-dependent dynamics of bacterial turbulence flows. Furthermore, by simultaneous fluorescent imaging of active swimming bacteria alongside passive tracers, we measure the relative contributions of self-swimming and background turbulent flow in the transport of an individual bacterium at different local availabilities of oxygen. We construct a mathematical model incorporating diffusion and consumption of oxygen along with advection due to bacterial turbulence that explains our experimental observations. Our work helps elucidate the role of collective motion and nutrient consumption in the transport of nutrients through a population of bacteria.