Cell Shape and Budding Polarity as Drivers of Yeast Colony Expansion on Surfaces

Microbial colonies and biofilms on surfaces encounter distinct evolutionary dynamics and selective pressures compared to planktonic populations. Cells in these dense communities experience mechanical interactions from neighboring proliferating cells, which influence survival of lineages as they compete for space and nutrients. To investigate adaptive evolution in this context, we conducted an evolution experiment in the budding yeast Saccharomyces cerevisiae, selecting for faster colony expansion rates. Along with increased colony expansion rates, cells evolved an elongated cell shape and a bipolar budding pattern. Using a combination of sexual reproduction of an evolved clone with a wildtype, meiosis, sequencing, and segregant analysis, we identified mutations linked to cell elongation in genes that regulate the cell cycle, nutrient sensing, and budding polarity. We reconstructed these mutations into the wildtype to confirm their genetic causality for the evolved phenotypes and assess how these single-cell phenotypes affect colony morphology and expansion dynamics. This work sheds light on how changes in cell shape and budding polarity affect yeast colony morphology and expansion rate, providing insights into adaptive evolution of surface-bound microbial populations.