Josh Tasoff: Claremont Graduate University School of Politics and Economics

A significant fraction of all life in the biosphere exists in complex communities in which crossfeeding is essential. In the same way that firms and consumers exchange a vast array of goods in modern markets, organisms exchange essential resources to promote their growth. Here, we present a framework based on general equilibrium theory from economics to predict the population dynamics of crossfeeding microbial communities. Analysis of a special case of the model involving two crossfeeding microbes yields several novel insights: (1) the economic concept of comparative advantage is a crucial condition for trade-based mutualism between species, (2) species that contribute more resources increase their growth rate but at the expense of a lower share of the total population, and (3) the inability to produce essential metabolites (i.e. auxotrophy) can be a selective advantage that explains its prevalence in microbial ecosystems. To test our model experimentally, we construct a synthetic syntrophic consortia of Escherichia coli and manipulate the cells’ ability to exchange essential amino acids. Experimental data are consistent with those generated by our model. This biotic economics framework provides a foundation to tackle key questions in microbial ecology and evolution and has useful applications to engineering synthetic ecosystems.