  This fluid dynamics video presents three-dimensional kinetic simulations of
the dynamics in suspensions of oxytactic bacteria confined in thin liquid film
surrounded by air. At the initial time, the bacterial concentration is uniform
and isotropic, and there is no oxygen inside the film. The spatio-temporal
dynamics of the oxygen and bacterial concentration are analyzed. For small film
thicknesses, there is a weak migration of bacteria to the boundaries, and the
oxygen concentration is high inside the film as a result of diffusion; both
bacterial and oxygen concentrations quickly reach steady states. Above a
critical film thickness, a transition to chaotic dynamics is observed and is
characterized by turbulent-like 3D motion, the formation of bacterial plumes,
enhanced oxygen mixing and transport into the film, and hydrodynamic velocities
of magnitude up to 7 times the single bacterial swimming speed. This collective
motion arises as a result of the combined effect of hydrodynamic interactions
and oxygentaxis, and may play a role in facilitating the access of bacteria to
oxygen in fluid environments.
