# Evolutionary adaptation of dense microbial populations to range expansion

> **NIH NIH F31** · CORNELL UNIVERSITY · 2024 · $48,974

## Abstract

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.

## Key facts

- **NIH application ID:** 10913345
- **Project number:** 5F31GM151814-02
- **Recipient organization:** CORNELL UNIVERSITY
- **Principal Investigator:** Katie Elaine Randolph
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $48,974
- **Award type:** 5
- **Project period:** 2023-08-01 → 2025-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10913345

## Citation

> US National Institutes of Health, RePORTER application 10913345, Evolutionary adaptation of dense microbial populations to range expansion (5F31GM151814-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10913345. Licensed CC0.

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