Linking Cell Morphology to the Collective Dynamics of Microbial Colonies

Surface-associated growth in the form of colonies and biofilms is a prevalent mode of microbial organization in natural environments. In non-motile organisms, cell-shape transitions under nutrient limitation are thought to facilitate surface colonization. Yet the link between single-cell morphology, the emergent material properties of these macroscopic assemblies, and their feedback on evolutionary dynamics remains poorly understood. To investigate this, we conducted an experimental evolution study in S. cerevisiae selecting for faster colony expansion on nutrient agar gels. This selection produced a striking morphological shift from the near-spherical ancestral cells to elongated, rod-shaped descendants. Using whole-genome sequencing and targeted reconstruction of causal mutations, we generated a collection of mutant strains spanning a range of cellular aspect ratios. This system allows us to characterize the effect of cell shape alone on emergent colony expansion dynamics and properties such as height profiles, expansion rates, biomass accumulation, and rheological behavior. Together, these results reveal how evolutionary changes at the single-cell level can reshape the mechanics and dynamics of microbial collectives, linking genotype, morphology, and material properties.