The impact of microscale fluid motion on the ecology of marine phytoplankton and soil bacteria

While many microorganisms spend their lives in moving fluids, fluid dynamics are often ignored when characterizing important ecological processes such as competition, predation, and the maintenance of diversity. In this talk, I will present laboratory experiments and mathematical models that illustrate how flow shapes the ecology of microbes by driving heterogeneity in their spatial distribution. First, I will show how turbulent flow ‘unmixes’ the distribution of motile phytoplankton. The resultant centimeter scale patches of phytoplankton are routinely observed in the ocean and have a profound impact on predation rates. Second, I will present experiments in which E. coli is inoculated in patterned microfluidic devices that simulate a porous soil environment. We find biofilm patches undergo a self-organization mediated by the interaction of growth and flow, leading to the formation of preferential flow channels. A model, which combines physics and game theory, predicts how this interaction facilitates competition between bacterial genotypes with different intrinsic growth rates.