Formate, a simple organic acid known to support chemotrophic hyperthermophiles, is found in hot springs of varying temperature and pH. However, it is not yet known how metabolic strategies that use formate could contribute to primary productivity in hydrothermal ecosystems. In an effort to provide a quantitative framework for assessing the role of formate metabolism, concentration data for dissolved formate and many other solutes in samples from Yellowstone hot springs were used, together with data for coexisting gas compositions, to evaluate the overall Gibbs energy for many reactions involving formate oxidation or reduction. The result is the first rigorous thermodynamic assessment of reactions involving formate oxidation to bicarbonate and reduction to methane coupled with various forms of iron, nitrogen, sulfur, hydrogen, and oxygen for hydrothermal ecosystems. We conclude that there are a limited number of reactions that can yield energy through formate reduction, in contrast to numerous formate oxidation reactions that can yield abundant energy for chemosynthetic microorganisms. Because the energy yields are so high, these results challenge the notion that hydrogen is the primary energy source of chemosynthetic microbes in hydrothermal ecosystems.

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Storage of CO2 through mineral sequestration using olivine has been shown to produce environmentally benign carbonates. However, due to the formation of a rate-limiting reaction product layer, the rate of reaction is insufficient for large-scale applications. We report the results of altering the reactant solution composition and the resultant reaction mechanism to enhance the reaction rate. The products were analyzed for total carbon content with thermal decomposition analysis, product phase compositions with Debye-Scherrer X-ray powder diffraction (XRD), surface morphology with scanning electron microscopy (SEM), and composition with energy dispersive X-ray spectroscopy (EDXS). Carbon analysis showed that an increase in bicarbonate ion activity increased the olivine to carbonate conversion rate. The fastest conversion rate, 63% conversion in one hour, occurred in a solution of 5.5 M KHCO3. Additionally, SEM confirmed that when the bicarbonate ion activity was increased, magnesium carbonate product particles significantly increased in both number density and size and the rate passivating-reaction layer exfoliation was augmented.

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Although microbial studies in hot spring environments are numerous, widespread surveys of the microbial diversity of thermal features are lacking. Many studies of hot spring environments have focused on a single organism or type of spring. In order to expand our knowledge of the extent of thermophilic life, we conducted a microbial inventory of thermal features in Yellowstone National Park that included in-depth geochemical measurements. We have analyzed microbial communities from greater than 40 thermal features from across YNP by 16S rRNA gene analysis of environmental DNA. These samples span the range of temperature and pH (48.9 -86.2°C and 2.00 -9.19) encountered in the park's thermal features. By combining phylogenetic analyses with geochemical data, we attempt to determine the level of control that the geochemistry of a spring exerts on the microbial communities. The relationship between community and geochemistry is strongest when the microbial communities are compared at the genus level. Temperature and pH are correlated with community structure, but do not alone predict the type of organisms present in a spring. Additional geochemical controls include both putative metabolically informative compounds (i.e. SO = 4 and NH + 4 ) and trace elements (i.e. F, Sr, Sb). Our geochemical approach includes computation of the state of disequilibrium for coupled redox reactions that represent possible energy-yielding reactions for microbial metabolism. Often, the highest energy yields are for hydrogen and sulfur oxidation: both pathways are known to be employed by Aquificales which dominate many of the sampled springs. Our ongoing work pairs communities with site-specific energy-yield characteristics. These results suggest niche control over community structure at the genus level. However, the much weaker relationship between geochemistry and species level groups suggests other mechanisms such as dispersal between springs or in situ evolution or mutation is affecting the individual populations that comprise the communities.