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Title
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Biogeochemistry of environmental gradients in serpentinization-influenced groundwater at the Coast Range Ophiolite Microbial Observatory, California
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Creator
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Sabuda, Mary C.
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Date
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2017
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Collection
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Electronic Theses & Dissertations
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Description
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Serpentinization of ultramafic rock in ophiolite complexes along continental margins leads to the mobilization of volatiles and reduced carbon compounds that can be used as sources of energy by subsurface microbial communities. The extent to which sulfur compounds can serve as electron acceptors in anoxic serpentinizing systems and their role in biogenic carbon cycling remains to be elucidated. Large scale processes at CROMO were studied using geochemical analyses, bioenergetics calculations,...
Show moreSerpentinization of ultramafic rock in ophiolite complexes along continental margins leads to the mobilization of volatiles and reduced carbon compounds that can be used as sources of energy by subsurface microbial communities. The extent to which sulfur compounds can serve as electron acceptors in anoxic serpentinizing systems and their role in biogenic carbon cycling remains to be elucidated. Large scale processes at CROMO were studied using geochemical analyses, bioenergetics calculations, microscopic cell counts, and 16S rRNA sequencing to identify the population of sulfate reducers and methane cyclers. Shotgun metagenomic and metatranscriptomic sequencing identified the production of key genes for sulfate reduction, sulfide oxidation, and thiosulfate disproportionation. Small scale processes at CROMO were identified through a depth profile of CSW1.1. With water pumped directly from the well, microcosms were created to measure the growth of microbial communities in the presence of 13CH4. Thiosulfate or Fe(OH)3 were injected as electron acceptors, with the addition of O2 gas in designated “oxic” bottles. The highest cell growth and biogenic 13DIC production occurred in “anoxic” 13CH4 + thiosulfate amended bottles, with Trueperaceae dominating both the profile of CSW1.1 and the microcosms. The biogeochemistry of CROMO yields insight into the potential for sulfur and methane cycling within this cryptic serpentinite environment found throughout the world.
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Title
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Biofilms and beyond : characterizing novel cyclic di-GMP controlled phenotypes in Vibrio cholerae
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Creator
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Fernandez, Nicolas Luis
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Date
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2019
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Collection
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Electronic Theses & Dissertations
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Description
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"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...
Show more"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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Title
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Bioethics and moral expertise as a collective enterprise
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Creator
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McLeskey, Chet
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Date
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2017
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Collection
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Electronic Theses & Dissertations
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Description
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Moral expertise is not a fantasy contrived by those who would wish to wield it. Moral expertise is something that is achieved through training and experience, just as any other form of expertise. While it shares many features with other forms of expertise, it carries with it a form of authority that is different and distinctive due largely to its inherently normative nature. I examine moral expertise by first examining expertise itself. Given what we understand about expertise, how it is...
Show moreMoral expertise is not a fantasy contrived by those who would wish to wield it. Moral expertise is something that is achieved through training and experience, just as any other form of expertise. While it shares many features with other forms of expertise, it carries with it a form of authority that is different and distinctive due largely to its inherently normative nature. I examine moral expertise by first examining expertise itself. Given what we understand about expertise, how it is achieved, and the impacts it has on the cognition of those who achieve it, I claim that moral expertise in bioethics is best seen as something achieved by groups rather than individuals.
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