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Title: Abiotic Influences on Free-Living Microbial Communities in Hydrothermal Vent Ecosystems
Abstract: Hydrothermal vent ecosystems are defined by steep thermal and chemical gradients. Chemosynthetic microorganisms are the primary producers in these systems, utilizing the available chemical energy to support substantial animal biomass. The variety of chemical substrates provided by hydrothermal fluid and the surrounding seawater enables a metabolically diverse community of microbes. However, our understanding of how abiotic factors such as temperature, geochemistry, and mineral substrate influence the activity of these microbes is limited. The overarching goal of this dissertation is to examine the influence that these abiotic factors have on free-living microbial community composition, structure, and function. In this work I first examined the influence of temperature on primary productivity by using radio isotopic tracer studies to measure rates of carbon fixation by epi- and endolithic microbial communities from vent chimney sulfides. I show evidence that these communities fix more carbon at low temperatures, underscoring the importance of low temperature habitats in these environments characterized by high temperature. I then utilized in situ RNA preservation to examine community-wide microbial activity in low temperature vent fluids throughout a vent field. These data show two distinct activity profiles that cross-cut canonical habitat descriptions, and highlight the importance of the intra-field waters among the discrete vents as regions of high primary productivity similar to plumes emanating from high temperature chimneys. Finally, I designed novel colonization devices to examine the influence of mineral substrate on microbial community composition, structure, and succession. Mineralogy appeared to exert significant influence on certain taxa. I also identified potential early and late successional taxa. The combination of metabolic rate measurements, metatranscriptomics, and colonization experiments presented here, all with co-registered geochemistry, underscore the substantial heterogeneity of these systems and offer insight into the relative strengths of the abiotic forces that help to govern these ecosystems.