Host: Prof. Peter Yunker

Title: Evolutionary dynamics of non-motile cells growing on surfaces

Abstract:

Surface-associated microbial populations are ubiquitous in nature and display evolutionary dynamics that are not yet well characterized, despite their importance to human health and technology. Dense populations of non-motile microbes expand on surfaces by cell growth and division, while interacting mechanically with neighboring ones. In this talk, I will show that mechanical forces among proliferating cells reduce the power of natural selection in microbial colonies, prolonging the survival of deleterious mutations and reducing the rate at which beneficial mutations expand in these populations. These mechanical interactions also favor the maintenance of genetic diversity in colonies growing in time-varying environments. Additionally, I will present evidence that evolutionary adaptation can change the way in which cells interact mechanically with each other. By repeatedly propagating cells from the periphery of Saccharomyces cerevisiae colonies and using them to initiate new colonies, we have observed significant changes in cell shape and budding polarity, with cells becoming progressively more elongated with time. These adaptations lead to altered mechanical interaction between cells and may promote faster colony expansion. The evolutionary insights from our research may have implications for our understanding of pathogenic yeast strains, many of which are characterized by an elongated cell shape that is presumed to enhance their ability to infiltrate host tissues.