Limitation by a shared mutualist promotes coexistence of multiple competing partners

Although mutualisms are often studied as simple pairwise interactions, they typically involve complex networks of interacting species. How multiple mutualistic partners that provide the same service and compete for resources are maintained in mutualistic networks is an open question. We use a model bacterial community in which multiple 'partner strains' of Escherichia coli compete for a carbon source and exchange resources with a 'shared mutualist' strain of Salmonella enterica. In laboratory experiments, competing E. coli strains readily coexist in the presence of S. enterica, despite differences in their competitive abilities. We use ecological modeling to demonstrate that a shared mutualist can create temporary resource niche partitioning by limiting growth rates, even if yield is set by a resource external to a mutualism. This mechanism can extend to maintain multiple competing partner species. Our results improve our understanding of complex mutualistic communities and aid efforts to design stable microbial communities. Mutualists benefit their partners by providing resources that would be difficult to obtain independently. Here, the authors show in a bacterial community and with mathematical modeling how a mutualist can promote coexistence between competitors by providing them with different limiting resources.

Automated summary

The study shows that in a bacterial community, mutualists can promote coexistence among competitors by providing them with different limiting resources, as demonstrated through mathematical modeling.