Co-Existence Slows Diversification in Experimental Populations of E. coli and P. fluorescens

Microbes grown in heterogeneous laboratory environments can rapidly diversify into multiple, coexisting variants. While the genetic and evolutionary mechanisms of laboratory adaptive radiations are well studied, how the presence of other species alters the outcomes of diversification is less well understood. To test the effect of co-culture growth on the Pseudomonas fluorescens SBW25 adaptive radiation, Escherichia coli and P. fluorescens were cultured in monoculture and co-culture for 8 weeks. In P. fluorescens monoculture, Wrinkly and Smooth Spreader types rapidly evolved and were maintained over 8 weeks, while E. coli monocultures evolved two colony types, a big and a small colony variant. In contrast, we found that in co-culture, E. coli did not evolve small colony variants. Whole genome sequencing revealed the genetic basis of possible co-culture specific adaptations in both E. coli and P. fluorescens. Altogether, our data support that the presence of multiple species changed the outcome of adaptive radiation.