Emergence of cooperative behavior in microbial consortia

Abstract

Cooperative microbial communities and their impact are ubiquitous in nature. The complexities of the cross-feeding interactions within such communities invite the application of mathematical models as a tool which can be used to investigate key influences in the emergence of cooperative behavior and increased productivity of the community. In this work, we develop and investigate a differential equation model of competition within a chemostat between four microbial strains utilizing a substrate to produce two necessary metabolites. The population of our chemostat includes a wild type strain that generalizes in producing both metabolites, two cross-feeding cooperator strains that each specialize in producing one of the two metabolites, and a cheater strain that produces neither metabolite. Using numerical methods we consider three key characteristics of the microorganisms and investigate the impact on the emergence of mutual cross-feeding in the community. First, we investigate the impact that substrate input concentration and the rate and type (active vs. passive) of metabolite transport between cells has on the emergence of cooperation and multi-stabilities resulting from the competition. Second, we investigate the role that resource allocation within metabolic pathways plays in the results of the competition between cells with different metabolite production strategies. Introducing metabolite production cost into the model leads to new outcomes of the competition, including stable coexistence between different strains. Lastly, we examine the effect that an initial population of a non-cooperative cheater strain has on the outcome of competition. Our results show that the emergence of a cross-feeding consortia relies on the availability and efficient use of resources, ease of transport of metabolites between cells, and limited existence of cheaters.