Doctoral Dissertations
Date of Award
8-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Biochemistry and Cellular and Molecular Biology
Major Professor
Gladys M Alexandre
Committee Members
Brad Binder, Andreas Nebenführ, Erik Zinser
Abstract
Some bacteria utilize chemotaxis signaling pathways to alter flagellar swimming direction based on sensing of extracellular chemical gradients. Chemotaxis signaling confers an evolutionary advantage, particularly in competitive and chemically complex environments, such as the soil rhizosphere near plant roots. Due to its importance for bacterial survival, much work has gone into elucidating the roles of chemotaxis signaling in mediating swimming direction changes. However, other work has demonstrated that these chemotaxis systems can play additional and unexpected roles in bacterial physiology. These alternative functions of chemotaxis systems are often mediated via protein interactions with other signaling pathways, and these alternative functions are relatively less studied than the conventional roles of chemotaxis systems. We begin this dissertation with a literature review that summarizes non-chemotactic effects of chemotaxis systems, as well as any relevant protein interaction partners that are responsible for mediating these effects. We further speculate on the broadly conserved signaling paradigms that these interactions represent.
Additionally, we characterize the organization and alternative functions of the chemotaxis signaling systems in the beneficial soil bacterium and plant symbiont, Rhizobium leguminosarum biovar viciae 3841. Here, we show the unexpected finding that the deletion of chemotaxis genes alters cell metabolism of R. leguminosarum. We further show that chemotaxis proteins physically interact with a metabolic regulatory protein, PtsN, which results in both altered function of chemotaxis systems as well as altered function of PtsN. Additionally, we provide evidence that chemotaxis proteins alter the function of a different metabolic regulatory pathway, the PII signaling pathway, in a mechanism that likely involves protein-protein interactions. We also elucidate novel roles of chemotaxis signaling in flagellar biosynthesis and characterize the effects of two kinases in the chemotaxis pathway, CheA1 and CheA2, on mediating chemotactic output. Last, we conduct experiments to probe protein-protein interactions between chemotaxis proteins encoded in separate operons in R. leguminosarum. The data provide evidence that chemotaxis proteins from either operon can mix together inside of large macromolecular chemotaxis signaling arrays. Together, these data provide insight into novel functions of chemotaxis signaling pathways in a beneficial soil microbe.
Recommended Citation
Tinkey, Christopher M., "Elucidating Organization and Alternative Functions of Chemotaxis Systems in Rhizobium leguminosarum biovar viciae 3841. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/12778