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Item Influence of lithogenic energy on subglacial microbial community composition(Montana State University - Bozeman, College of Agriculture, 2021) Dunham, Eric Corwin; Chairperson, Graduate Committee: Eric Boyd; John E. Dore, Mark L. Skidmore, Eric E. Roden and Eric S. Boyd were co-authors of the article, 'Lithogenic hydrogen supports microbial primary production in subglacial and proglacial environments' in the journal 'Proceedings of the National Academy of Sciences of the United States of America' which is contained within this dissertation.; K. Rebecca Mitchell, Mark L. Skidmore and Eric S. Boyd were co-authors of the article, 'Influence of ferric iron on community composition in a basaltic glacial catchment' which is contained within this dissertation.Chemosynthesis, the generation of biomass using chemical energy, supported life on early Earth and continues to sustain contemporary light-independent ecosystems. The mechanisms of nutrient release from the geosphere are critical to understanding the present and historical distribution and diversity of life. Glaciers release such nutrients through comminution of bedrock, continuously resurfacing reactive minerals that can be colonized and exploited by chemosynthetic microorganisms. Bedrock mineralogy influences the nutrients available in these environments, but little is known about which nutrients are most important or how they affect microbial community composition, particularly in catchments overlying igneous bedrock like basalt. Iron and silicate minerals, common in basalt, readily generate both reductants such as H 2 and oxidants such as Fe(III) through interactions with water. Abundant H 2 in meltwaters of the basalt-based Icelandic glacier Kotlujokull (KJ) were found to support sediment microbial communities better adapted to use H 2 in chemosynthetic metabolism than those found beneath the carbonate-based Robertson Glacier (RG), Canada. KJ communities exhibited shorter lag-times and faster rates of net H 2 oxidation and dark carbon dioxide (CO 2) fixation than those from RG. A KJ sediment enrichment culture provided with H 2, CO 2, and Fe(III) produced a chemolithoautotrophic population related to Rhodoferax ferrireducens, which was also detected using molecular techniques in sediments from Kaldalonsjokull (Kal), another basalt-based Icelandic glacier. The abundance and composition of microbial communities that colonized defined minerals incubated for 12 months in Kal meltwater streams were examined by extracting DNA and sequencing PCR-amplifiable 16S rRNA genes. DNA quantities and the composition of 16S rRNA genes recovered from Kal sediments were most similar to those recovered from incubated Fe(III)-bearing minerals hematite and magnetite, with putative Fe(III) reducers dominating all three communities. These findings point to the importance of bedrock mineral composition in influencing the supplies of nutrients like H 2 and Fe(III) that, in turn, influence the diversity, abundance, and activity of microbial communities in subglacial environments. They further indicate the potential for subglacial habitats to serve as refugia for microbial communities in the absence of sunlight, such as during Snowball Earth episodes, or on icy planets without photosynthetic life.Item Inorganic carbon fixation and trophic interactions in high-temperature geothermal springs of Yellowstone National Park, WY, USA(Montana State University - Bozeman, College of Agriculture, 2015) Jennings, Ryan deMontmollin; Chairperson, Graduate Committee: William P. Inskeep; Laura M. Whitmore, James J. Moran, Helen W. Kreuzer and William P. Inskeep were co-authors of the article, 'Carbon dioxide fixation by metallosphaera yellowstonensis and acidothermophilic iron-oxidizing microbial communities from Yellowstone National Park' in the journal 'The American Society for Microbiology Applied and Environmental Microbiology journal' which is contained within this thesis.; James J. Moran, Zackary J. Jay, Jacob P. Beam, Laura M. Whitmore, Mark A. Kozubal, Helen W. Kreuzer, and William P. Inskeep were co-authors of the article, 'The extent and mechanisms of carbon dioxide fixation across geochemically diverse high-temperature microbial communities' submitted to the journal 'Nature publishing group nature geosciences journal' which is contained within this thesis.; Kristopher A. Hunt, Ross P. Carlson and William P. Inskeep were co-authors of the article, 'Genome-enabled multi-scale analysis of autotroph-heterotroph interactions in a high-temperature microbial community' submitted to the journal 'The International Society for Microbial Ecology journal' which is contained within this thesis.Numerous chemotrophic microorganisms inhabit high-temperature (> 65 °C) systems of Yellowstone National Park (WY, USA). Prior geochemical and metagenome characterization has identified the primary electron donors and acceptors and phylotypes distributed across a range in pH and geochemical conditions. Although several chemolithoautotrophs are expected to play a direct role in the fixation of inorganic C in these communities, little work has directly identified the importance of this process in situ. Consequently, the primary goal of this thesis was to evaluate the role of CO 2 fixation across numerous types of geothermal habitats and to explore autotroph-heterotroph interactions that may control community composition. Genes encoding enzymes for inorganic C fixation pathways were identified in assembled genome sequence corresponding to the predominant autotrophs (Crenarchaeota and Aquificales) observed in Fe(III)-oxide mats, sulfur sediments, and filamentous streamer communities. Carbon isotope (13 C) mixing models were used to interpret the 13C compositional values of microbial samples as a function of 13C-dissolved inorganic C (DIC) and 13 C-organic C (DOC and/or landscape sources). The relative abundance of autotrophs versus heterotrophs identified in complementary metagenome analysis and respective CO 2-fixation fractionation factors were utilized in site-specific mixing models to calculate minimum contributions of DIC-derived microbial C across 15 different microbial communities. Genome sequence was also used to develop stoichiometric reaction networks for a primary autotroph (Metallosphaera yellowstonensis) and heterotroph ('Geoarchaeota') important in acidic Fe(III)-oxide mats. Possible modes of biomass production were evaluated for different C sources and/or electron donors as a function of oxygen cost. The total oxygen flux was also used to predict the rate of Fe(II)-oxidation, and these values were compared to Fe(III)-oxide deposition rates and oxygen fluxes measured in situ. Stoichiometric modeling and elementary flux mode analysis established an optimum autotroph to heterotroph ratio (2.4:1) for DIC-derived biomass dependent on Fe(II) as the electron donor. Comparison of predicted Fe(II)-oxidation rates with observed Fe(III)-oxide deposition rates and oxygen flux measurements using microelectrodes suggest the importance of other oxygen consuming processes. Results from this thesis demonstrated the importance of inorganic C fixation in numerous geochemically distinct high-temperature microbial habitats, and the potential for DIC-derived biomass to support other hyperthermophilic heterotrophic organisms.Item Chemosynthetic carbon metabolism in thermophiles(Montana State University - Bozeman, College of Letters & Science, 2015) Urschel, Matthew Robert; Chairperson, Graduate Committee: Eric Boyd; Michael D. Kubo, Tori M. Hoehler, John W. Peters and Eric S. Boyd were co-authors of the article, 'Carbon source preference in chemosynthetic hot spring communities' in the journal 'Applied and Environmental Microbiology' which is contained within this thesis.; Matthew R. Urschel, Trinity L. Hamilton, Eric E. Roden and Eric S. Boyd were co-authors of the article, 'Substrate preference and uptake kinetics in a facultatively autotrophic and hyperthermophilic crenarchaeote' submitted to the journal 'Applied and environmental microbiology' which is contained within this thesis.Microbial communities inhabiting high temperature (>73°C) environments are supported by chemical energy, providing a unique opportunity to investigate the processes that supported life prior to the advent of photosynthesis. Previous work has focused on the importance of autotrophy in supporting such communities, and recent reports of organic substrate utilization in several high temperature springs in Yellowstone National Park (YNP), Wyoming, USA suggest that chemosynthetic populations are facultatively autotrophic. Nevertheless, little is known about the factors influencing relative rates of autotrophy and heterotrophy in these systems, and few studies have addressed the potential role of facultative autotrophs in supporting these ecosystems. This work addressed these compelling questions using in situ microcosm assays to directly quantify organic and inorganic substrate transformation rates in 13 geochemically diverse YNP chemosynthetic communities. The results provide the first conclusive evidence that dominant autotrophs in these ecosystems are facultative, and can alter their metabolism over short time spans to preferentially exploit more thermodynamically favorable organic substrates at rates comparable to or exceeding those of inorganic substrate utilization. Multivariate statistical analysis of co-registered substrate transformation rates, geochemical measurements, and phylogenetic data collected from these communities suggests an important relationship between environmental variation, community composition, and the relative importance of autotrophic and heterotrophic metabolisms supporting these communities. Elevated formate utilization rates in crenarchaea-dominated chemosynthetic communities inhabiting acidic, sulfur-rich geothermal springs motivated the isolation of the first hyperthermophilic crenarchaeon (Thermoproteus sp CP80) capable of coupling formate oxidation to elemental sulfur reduction. Physiological characterization demonstrated that CP80 is a facultative autotroph that alters its metabolism to preferentially utilize formate over CO 2. Similar formate utilization characteristics by CP80 and its native population strongly suggests that this and other sulfur reducing crenarchaea may be responsible for high rates of formate utilization in high temperature, sulfur rich YNP systems. Overall, these results indicate an important, previously-underestimated role for organic substrates in supporting chemosynthetic communities inhabiting geochemically diverse YNP hot springs. Future work should focus on identifying additional organic carbon sources, measurement of carbon flux through chemosynthetic communities, and further characterization of the biochemical mechanisms underlying organic and inorganic substrate metabolismin Thermoproteus sp. CP80.