Dispersal of a dominant competitor can drive multispecies coexistence in biofilms

Despite competition for both space and nutrients, bacterial species often coexist within structured, surface-attached communities termed biofilms. While these communities play important, widespread roles in ecosystems and are agents of human infection, understanding how multiple bacterial species assemble to form these communities and what physical processes underpin the composition of multispecies biofilms remains an active area of research. Using a model three-species community composed of P. aeruginosa, E. coli, and E. faecalis, we show with cellular scale resolution that biased dispersal of the dominant community member, P. aeruginosa, prevents competitive exclusion from occurring, leading to coexistence of the three species. A P. aeruginosa bqsS deletion mutant no longer undergoes periodic mass dispersal, leading to local competitive exclusion of E. coli. Introducing periodic, asymmetric dispersal behavior into minimal models parameterized by only maximal growth rate and local density supports the intuition that biased dispersal of an otherwise dominant competitor can permit coexistence generally. Colonization experiments show that WT P. aeruginosa is superior at colonizing new areas in comparison to{Delta} bqsS P. aeruginosa, but at the cost of decreased local competitive ability against E. coli and E. faecalis. Overall, our experiments document how one species modulation of a competition-dispersal-colonization trade-off can go on to influence the stability of multispecies coexistence in spatially structured ecosystems.