Dynamically induced spatial segregation in multispecies bacterial bioconvection

Active matter, from motile bacteria to animals, can exhibit striking
collective and coherent behavior. Despite significant advances in
understanding the behavior of homogeneous systems, little is known about
the self-organization and dynamics of heterogeneous active matter, such as
complex and diverse bacterial communities. Under oxygen gradients, many
bacterial species swim towards air-liquid interfaces in auto-organized,
directional bioconvective flows, whose spatial scales exceed the cell size
by orders of magnitude. Here we show that multispecies bacterial
suspensions undergoing oxytactic-driven bioconvection exhibit dynamically
driven spatial segregation, despite the enhanced mixing of bioconvective
flows, and the fact that these species coexist in their natural habitat.
Segregation is observed as patterns of spatially interlocked domains, with
local dominance of one of the constituent species in the suspension. Our
findings suggest that segregation mechanisms involve minimization of
collisions under conditions of hydrodynamic flow rather than biological
repulsion. Thus, species with different motile characteristics in the same
ecological context can enhance their access to limiting resources. This
work provides novel insights on the role of heterogeneity in active
matter, as well as on the dynamics of complex microbial communities, their
spatial organization and their collective behavior.