"The second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) is often utilized by bacteria to transduce external information inside the cell to allow the appropriate response. Soon after investigations began, the connection between c-di-GMP signaling and the transition between sessile and motile lifestyles became clear. Numerous reports demonstrate c-di-GMP promotes production of the biofilm matrix while simultaneously decreasing motility through diverse mechanisms. Researchers also identified c-di-GMP as a signal in other cellular processes in organisms with niche specific phenotypes such as promoting asymmetric cell division, differentiation, predation, and pathogenesis. However, with such vast signaling networks in some bacteria, whether c-di-GMP had a larger influence on controlling cell behavior was to be determined.In this work, I provide examples of how the aquatic organism and human pathogen Vibrio cholerae utilizes c-di-GMP signaling to connect disparate cell behaviors with biofilm formation and explore how these behaviors could promote survival in its natural reservoir. This is exemplified in Chapters 2 and 3, where I demonstrate c-di-GMP increases tolerance to DNA damage and oxidative stress. Importantly, these responses were independent of biofilm matrix production, which can often provide protection from antimicrobials. My data indicate c-di-GMP specifically increases expression of genes involved in DNA repair and antioxidant production, which is sufficient to provide a growth advantage under stressful conditions. Additionally, these responses to increased c-di-GMP were dependent on a c-di-GMP dependent transcription factor, VpsT, which is responsible for biofilm matrix production. Thus, these data support a model where, under high c-di-GMP conditions, matrix production is co-regulated with DNA repair and antioxidant production, suggesting biofilm formation in V. cholerae involves a pre-emptive induction of stress responses, which could promote persistence in the environment.In chapter 4, I uncover an important, previously unrecognized, role for c-di-GMP signaling: control of cell shape to promote biofilm formation. V. cholerae adopts a vibrioid, or curve-rod, appearance which was first observed by early microbiology pioneers in the 1800's. Further examination by Arthur Henrici in 1928 found that V. cholerae shape is heterogenous and was influenced by growth phase. However, how V. cholerae regulated its shape change and the ecological benefits of such changes remained a mystery. In this work, I found that high c-di-GMP concentrations caused the straightening of the vibrioid shape. Disrupting this process by forcing cells to remain curved during surface colonization caused defects in biofilm formation. By using single-cell analysis, my work suggests curvature causes irregularities in cell-to-cell contact during the early stages of biofilm formation. In summation, by orchestrating matrix production, stress responses, and cell shape changes, my results indicate c-di-GMP plays a global role in V. cholerae by preparing cells as they transition to the biofilm lifestyle."--Pages ii-iii.
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