Self-concentration and large-scale coherence in bacterial dynamics

The collective effects in bacterial suspensions in which strong microscale mixing arises from self-concentration and large-scale dynamic coherence were described. Self-concentration arose from chemotactically generated accumulations of cells that encounter, then slide down a slanted meniscus, resulting in even higher concentrations. The consumption of dissolved oxygen by cells and its replenishment from the fluid-air interface sets the stage for bioconvection. The results show that in the concentrated regime the temporal evolution must include an advective component, the fluid velocity determined self-consistently with the density.