Shearing in flow environment promotes evolution of social behavior in microbial populations

It is advantageous for microbes to form social aggregates when they commonly benefit from secreting a public good. However, cooperating microbial groups can be evolutionarily unstable, since a cheating strain that does not secrete the public good can reproduce quicker and take over. Here we study the effects of fluid advection patterns on group reproduction as a mechanism to enable or enhance social behavior in microbial populations. We use a realistic advection-diffusion-reaction model to describe microbial growth and mutation in a flow environment. Social groups arise naturally from our model as self-reproducing Turing patterns that can avoid mutant takeovers at steady state. Our central finding is that flow shear enables and promotes social behavior in microbes by limiting the spread of cheating strains. Regions of the flow domain with higher shear admits high cooperativity and large population density, whereas low shear regions are devoid of life due to opportunistic mutations.