The motility can drive spatial exclusion and promote coexistence in bacterial populations

Bacterial cells encountered in nature rarely live in isolation, they share and compete for space and nutrients with cohabitant microbial communities. They are also known to explore their surroundings and exhibit motility. Despite the ubiquity of motile phenotypes, the fundamental role of bacterial dispersal in the formation of diverse microbial communities and coexistence in spatial habitats have not been elucidated. In this study, we investigated the motility-driven competition for resources between two strains resulting in strong negative frequency-dependent-selection, i.e. each strain becomes fitter than the other when low in frequency. The observed lack of competitive exclusion is a direct consequence of the active segregation: few fast movers can forage and rapidly colonize in virgin territories of the habitat whereas few fast-grower cells can proliferate at the initial contact position. We showed that the coexistence breaks down when the initial contact area is as large as the habitat size or the nutrients become available homogeneously. Our findings demonstrate that motility can foster coexistence between bacterial populations displaying growth-dispersal trade-off in competition for nutrients and space.