Guillemin, KarenRobinson, CathyGallagher, DaphneMa, Emily2021-07-272021-07-272021https://hdl.handle.net/1794/2654135 pagesAnimals are colonized by communities of microorganisms that influence the health and development of their host. However, the mechanisms of host colonization are still underexplored. To investigate this, previous work in the lab used experimental evolution to adapt a bacterial symbiont, Aeromonas, to the zebrafish gut. These experiments led to the identification of a novel gene, spdE, which significantly impacts host colonization. We found that evolved isolates with mutations in spdE had faster rates of motility and increased host immigration. Sequence analysis revealed that the protein, SpdE, has a domain for sensing extracellular signals and a diguanylate cyclase domain which produces an intercellular signaling molecule that regulates motility. Further biochemical investigation identified that the signal SpdE senses is hydrophobic amino acids, specifically proline, valine, and isoleucine. To further investigate the relationship between SpdE-dependent Aeromonas motility and environmental amino acids, we developed a new technique (“exploration assay”) which is designed to measure differences in motility between strains or conditions. Using the exploration assay, we compared motility of wild type and spdE knockout strains in different amino acid environments. From our results, we found that the wild type strain is more motile in the presence of these amino acids. However, even in the absence of amino acid signal, the spdE knockout is more motile than the wild type. From these data, we have created a model for how SpdE regulates motility in response to amino acids which offers novel insights into Aeromonas biology and the mechanisms of host colonization.en-USCC BY-NC-ND 4.0Aeromonas veroniibacterial motilityZebrafishspdEhost colonizationThesis/Dissertation0000-0002-7694-0889