Evolutionary adaptation of dense microbial populations to range expansion

点击翻译按钮获取中文摘要

PROJECT SUMMARY 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. Genetic drift, the change in allele abundances due to chance alone, is known to be much more important in the surface-associated scenario than for microbes in well-mixed liquid media, but it is unknown which properties of cells and populations modulate this effect. I performed an evolutionary range expansion experiment with the budding yeast, Saccharomyces cerevisiae, to investigate how cells evolve when selected for more efficient surface-associated growth. We found that cells selected for faster expansion on surfaces evolved an elongated cell shape and a bipolar budding pattern, in which daughter cells bud at the pole opposite to the birth scar. Additionally, preliminary results suggest that evolved colonies display increased genetic drift compared to the ancestor. This proposal aims to understand the genetic changes that caused these phenotypes, and how these phenotypes modify the physical parameters of the system to enable faster expansion. Further, I will use this information to understand how properties of single cells affect the relative strength of natural selection and genetic drift in dense cellular aggregates. I hypothesize that the faster expansion is the result of evolved changes in physical properties of the colony that modify the way cells interact with each other and the agar surface. Additionally, I hypothesize that an elongated cell shape contributes to an increased strength of genetic drift in surface-associated growth. I will address this hypothesis by identifying the genes that cause each evolved phenotype, characterizing the physical properties of colonies and cells that affect expansion dynamics and three-dimensional colony structure, and finally use this information to assess the effect of each phenotypic change on the relative strength of genetic drift in expanding colonies. Completion of these goals will ensure I have developed expertise in both theoretical and experimental approaches pivotal to independent biophysical research with health-related applications, a major goal of my fellowship training plan. My training plan also includes training in scientific communication and inclusive teaching and mentorship. I will benefit from the significant resources granted to me by Cornell in the way of on-site, state-of-the-art research facilities, collaboration with experts specific to all fields represented in my research, and a wonderfully supportive research advisor, the sponsor of this work.