Evolutionary adaptation of dense microbial colonies to surface associated growth

Dense microbial aggregates such as a colony or biofilm experience mechanical interactions among cells that may affect their evolutionary dynamics by modulating the rate at which new mutations spread through the population. To explore how mechanical interactions affect colony evolutionary dynamics, we performed an evolution experiment with the budding yeast Saccharomyces cerevisiae in which we selected for faster colony expansion on a surface. We found that, in addition to expanding faster, evolved cells are strikingly more elongated than their ancestor and display a bipolar budding pattern, meaning that daughter cells may bud at the pole opposite the birth scar, unlike their ancestor. This work has detected the genetic basis for these phenotypic changes and reconstructed key evolved phenotypes in the wildtype ancestor to both confirm genetic causation of the phenotype and to identify which phenotypic trait contributes most significantly to the increased expansion velocity. Future work will investigate the physical and mechanical changes evolved at both the single-cell and colony scales that enable faster expansion and modulation of the evolutionary dynamics at play in the colony. Taken together, these data will provide a comprehensive understanding of evolutionary adaptation to surface-associated growth.