Investigating microbial specific growth rates and food web connectivity using experimental mesocosms, modeling, and genomics

The work within this project uses chemostat experiments to test several hypotheses related to specific growth rates, resource use, and food web connectivity in aquatic microbial communities. Maximum specific growth rate is an example of an important trait that determines if a microbe can persist within an environment where fluid transport advects organisms from the system. In our first chemostat experiment, we manipulated the dilution rate to test how it would act as a selective force controlling microbial community dynamics and diversity as assessed by 16S rRNA gene sequencing. We compared experimental results to output from two different simulations of trait-based modeling, one in which maximum specific growth rate is initially evenly distributed across the community and another where maximum specific growth rate traits are pulled from a beta probability distribution that is skewed towards low specific growth rates. Next, to test the hypothesis that microbial communities organize to form strongly coupled predator-prey chains that are weakly interconnected, we ran a series of chemostat experiments inoculated with natural microbial communities and different isotopically-labeled carbon substrates. Food web structure was assessed with stable isotope probing techniques and the active consumers and their predators identified by sequencing of the labeled community. Results from these experiments facilitate development of Darwin-based MEP models, contribute significantly to our theoretical understanding of how microbial communities organize to facilitate the dissipation of available free energy, and advance consumer-resource theory.