Energy transfer between the geosphere and biosphere

One goal of geobiochemistry is to follow geochemical energy supplies from the external environment to the inside of microbial cells. This can be accomplished by combining thermodynamic calculations of energy supplies from geochemical processes and energy demands for biochemical processes. Progress towards this goal is summarized here. A critique of all thermodynamic data for biochemical compounds involved in the citric acid cycle (CAC) and the formulation of metabolite properties allows predictions of the energy involved in each step of the cycle as well as the full forward and reverse cycles over wide ranges of temperature and pressure. These results allow evaluation of energy demands at the center of many microbial metabolic systems. Field work, sampling, and lab analyses from two low-temperature systems, a serpentinizing system, and a subglacial setting, provide the data used in these thermodynamic analyses of energy supplies. An extensive literature summary of microbial and molecular data from serpentinizing systems found is used to guide the evaluation and ranking of energy supplies used by chemolithoautotrophic microbes. These results constrain models of the distribution of microbial metabolisms throughout the low-temperature serpentinization systems in the Samail ophiolite in Oman (including locales of primary and subsequent alteration processes). Data collected from Robertson Glacier in Alberta, Canada, together with literature data from Lake Vida in Antarctica and bottom seawater, allowed thermodynamic analyses of low-temperature energy supplies in a glacial system. Results for 1460 inorganic redox reactions are used to fully inventory the geochemical energy sources that support the globally extensive cold biosphere.