Onset of bioconvection in suspensions of Bacillus subtilis

Bioconvection occurs when upward swimming micro-organisms generate gravitational energy that initiates and maintains dissipative movement of the water in which they swim. Advection, and motion of the organisms relative to the fluid, generate patchiness in concentration that drives and shapes the geometry and rate of convection. This paper presents a method for quantitatively analyzing the development of self-organization, and numerical estimates that connect and interpret theory and experiment. While the oxygen consuming, oxgen-gradient-guided bacteria Bacillus subtilis are the sole subject here, the methods developed will find application to the analysis and modeling of other complex dynamic systems that ineluctably combine physics and biology.