Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular, Cellular, and Developmental Biology

First Advisor

Emonet, Thierry

Abstract

Bacteria use a highly conserved sensory pathway to navigate chemical gradients. In particular, the chemotactic signaling pathway of Escherichia coli is one of the best-characterized systems in biology. However, despite decades of study, there are still open questions about bacterial chemotaxis, including how clusters of receptors cooperatively amplify signals, how variability in the composition of these arrays affects behavioral diversity, and how findings in E. coli generalize to diverse motile behaviors across bacteria. In this thesis, we explore diversity in chemosensory capabilities within and across bacteria species. First, we characterize the distribution of sensitivities to various chemical attractants in populations of E. coli, and how these distributions are shaped by adaptation to ambient chemical stimuli. Our findings are consistent with a model where the underlying distribution of receptor cooperativities varies from cell to cell, but a nonlinear mapping from cooperativity to sensitivity enables the population to utilize this diversity or not depending on ambient chemical signals. Second, we measure responses of the chemotaxis signaling pathway in Vibrio cholerae which, unlike E. coli which express multiple peritrichous flagella, have a single polar flagellum, enabling a distinct swimming pattern called ‘run-reverse-flick’. To our knowledge, this is the first time chemosensory responses have been directly measured in a polar-flagellated bacterium. Our findings reveal differences in the rate and accuracy of adaptation, as well as a surprisingly low cooperativity, which we interpret in the context of cholera’s swimming behavior.

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