Abstract
A kinetic model and three-dimensional numerical simulations are applied to study the dynamics in suspensions of run-and-tumble aerotactic bacteria confined in free-standing liquid films surrounded by air. In thin films, oxygen and bacterial concentration profiles approach steady states. In thicker films, a transition to chaotic dynamics is shown to occur and is characterized by unsteady correlated motions, the formation of bacterial plumes, and enhanced oxygen transport and consumption. This transition, also observed in previous experiments, arises as a result of the coupling between the aerotactic response of the bacteria and the flow fields they generate via hydrodynamic interactions.
Highlights
A kinetic model and three-dimensional numerical simulations are applied to study the dynamics in suspensions of run-and-tumble aerotactic bacteria confined in freestanding liquid films surrounded by air
A transition to chaotic dynamics is shown to occur and is characterized by unsteady correlated motions, the formation of bacterial plumes, and enhanced oxygen transport and consumption. This transition, observed in previous experiments, arises as a result of the coupling between the aerotactic response of the bacteria and the flow fields they generate via hydrodynamic interactions
In this Letter, we address this problem by extending a previous kinetic model for active suspensions[12,13,14] to account for run-and-tumble aerotaxis in thin liquid films, and explicitly model the three-way coupling between bacterial dynamics, oxygen transport, and fluid flow
Summary
Spectral analysis of mixing in chaotic flows via the mapping matrix formalism: Inclusion of molecular diffusion and quantitative eigenvalue estimate in the purely convective limit Phys. A transition to chaotic dynamics is shown to occur and is characterized by unsteady correlated motions, the formation of bacterial plumes, and enhanced oxygen transport and consumption This transition, observed in previous experiments, arises as a result of the coupling between the aerotactic response of the bacteria and the flow fields they generate via hydrodynamic interactions. Both effects drive the formation of oxygen gradients inside the film, to which the bacteria respond by modifying their run-and-tumble dynamics so as to migrate preferentially towards the oxygen-rich regions near the boundaries This aerotactic response leads to anisotropic orientation distributions, thereby inducing active stresses that, in some cases, can drive three-dimensional flows. 1(e) and 1(f)], regime III is characterized by a strong bacterial migration towards the boundaries and unsteady flow dynamics, and exhibits a strong oxygen depletion layer and an additional accumulation of bacteria near the center of the film (see Fig. 2). We consider base-state profiles of p zz and
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