Quantitative Biosciences Thesis Proposal
School of Biological Sciences
Advisor: Dr. Will Ratcliff (School of Biological Sciences)
Co-advisor: Dr. Brian Hammer (School of Biological Sciences)
Open to the Community
Cooperation and Conflict: aggregative multicellularity and defense against the T6SS
Monday, September 13, 2021 at 11:00 am
BlueJeans Link: https://bluejeans.com/746683505/0690
Dr. Frank Rosenzweig (School of Biological Sciences)
Dr. Sam Brown (School of Biological Sciences)
This thesis proposal consists of two independent projects:
● Adhesion and assortment during the evolution of aggregative multicellularity
● Experimental evolution of defense to the bacterial T6SS
Multicellular organisms develop through one of two basic modes: they can grow clonally, where cells stay together after division, or they can form an aggregative group from separate, potentially unrelated cells. Most of the prior work examining early steps in the evolution of multicellularity has focused on groups that develop clonally. My research will examine a key first step in the evolution of aggregative multicellularity- how genotypes become positively assorted within groups. Positive assortment is necessary for selection to act on group-level traits, but little prior work has examined how positive assortment initially arises in aggregative multicellularity. Here we propose the use of flocculating Saccharomyces cerevisiae (expressing the FLO1 gene) (1) to understand how simply increasing expression of a surface adhesin can generate positive assortment as a side-effect, and (2) to explore the mechanisms flocculating yeast evolve that drive positive assortment over ~1,000 generations of experimental evolution.
The Type VI Secretion System is a nano-harpoon, used to inject toxins into neighboring cells. Approximately 25% of all Gram negative species encode this weapon, each with a specialized set of toxins. While the mechanism of the T6SS attack is well understood, less is known about ways that cells can defend themselves against it. We performed experimental evolution on eight E. coli populations, exposing them to Vibrio cholerae’s T6SS daily for 30 days (~500 generations of growth), resulting in a ~100-fold increase of survival compared to the ancestor. However, all of these evolved strains have incurred a growth cost in rich media. In this proposal, we aim to (1) characterize the evolutionary tradeoff between T6SS resistance and growth rate using further experimental evolution and (2) explore the epistatic relationship between two genes that were mutated in parallel in two populations.