Geochemical constraints on microbial diversity of hydrothermal ecosystems in Yellowstone National Park

Microbial diversity in extreme environments is a topic at the forefront of many scientific questions. Developments in molecular biology over the last 25 years have dramatically expanded knowledge of microbial diversity and the extent of the biosphere on Earth, and the future holds exciting developments as more "extremophiles" are added to culture collections. Hydrothermal systems are extreme environments of great interest, and microbes living in these fluids, known as thermophiles, are the target of many investigations into the origins of life on Earth and potential life elsewhere in our Solar System. This body of work focuses on the interaction of thermophiles with hydrothermal systems in Yellowstone National Park, approaching the problem by analyzing the geochemical environment, the community composition, and the role of individual microbes in these ecosystems. The first chapter of this dissertation examines microbial communities in three geochemically distinct hot springs: Obsidian Pool, in the Mud Volcano area; Sylvan Spring, of the Gibbon Meadow Group; and "Bison Pool," a feature in the Lower Geyser Basin. The community compositions are examined by extracting 16S rRNA gene sequences from sediment samples, and the geochemically-defined environments are characterized with a focus on potential sources of metabolic energy. Chapter Two introduces a new methodology for culturing thermophilic organisms. This approach uses the geochemical composition of specific thermal features as a design template for aqueous growth media for the isolation of novel thermophiles, specifically examining the effect of trace element compositions on the cultured organisms. This method was used to isolate four novel organisms from Sylvan Spring, and the characterization of these organisms is the topic of the last chapter, which details their physiology. These isolates utilize a range of metabolic tactics and are all thermophiles adapted to live in the acidic fluids of Sylvan Spring. Two of the novel organisms are the most thermophilic acid-tolerant bacteria known in current culture collections. Using geochemistry as a point of reference for extremophilic communities is essential to comprehending the interaction of microbes with extreme environments and the future elucidation of the often unique metabolic pathways and adaptations of these organisms.