Microbial communities contain cells of different shapes, and yet we know little about how these shapes affect community biology. We have developed a computational model to study the effects of microbial shape in communities. Our model predicts that shape will have strong effects on cells’ positioning, and, consequently, their survival and reproduction. Rod-shaped cells are better at colonizing the base of the community and its expanding edges, whereas round cells dominate the upper surface. We show that the same patterns occur in colonies of Escherichia coli, using strains with different shapes. Our work suggests that cell shape is a major determinant of patterning and evolutionary fitness within microbial communities.

Abstract

The clearest phenotypic characteristic of microbial cells is their shape, but we do not understand how cell shape affects the dense communities, known as biofilms, where many microbes live. Here, we use individual-based modeling to systematically vary cell shape and study its impact in simulated communities. We compete cells with different cell morphologies under a range of conditions and ask how shape affects the patterning and evolutionary fitness of cells within a community. Our models predict that cell shape will strongly influence the fate of a cell lineage: we describe a mechanism through which coccal (round) cells rise to the upper surface of a community, leading to a strong spatial structuring that can be critical for fitness. We test our predictions experimentally using strains of Escherichia coli that grow at a similar rate but differ in cell shape due to single amino acid changes in the actin homolog MreB. As predicted by our model, cell types strongly sort by shape, with round cells at the top of the colony and rod cells dominating the basal surface and edges. Our work suggests that cell morphology has a strong impact within microbial communities and may offer new ways to engineer the structure of synthetic communities.