Abstract

The majority of bacteria live in porous substrates like soil, sediments, and aquifers. In this talk, I present laboratory experiments and mathematical models that illustrate how flow through these porous environments affects the ecology of bacteria. When we inoculate cells in porous microfluidic devices, we find they form biofilm patches that undergo a self-organization mediated by the interaction of growth and flow. At intermediate flow rates this interaction triggers the formation of preferential flow channels, which limit biofilm respiration rates. A simple network model, which captures the underlying physics, corroborates our experimental results. We then use this system to determine how pore scale hydrodynamics impact the competition between bacterial genotypes that grow at different rates. By combining a mechanistic model with game theory, we predict that porous media flow selects for bacteria with an ‘evolutionarily stable’ growth rate, which outcompete cells that grow either more quickly or more slowly. Our findings stand in sharp contrast to the commonly held assumption that a bacterial genotype’s fitness increases monotonically with its intrinsic growth rate.