Continental deep subsurface Targeted Locus (Loci)

In an effort to better understand the biogeochemistry of deep terrestrial habitats, a holistic evaluation of chemolithoautotrophic microbial metabolisms in the Sanford Underground Research Facility (SURF) in the former Homestake Gold Mine, SD, USA has been undertaken. Geochemical data, energetic modeling, and DNA sequencing of constituent microbial populations have been combined with Principle Component Analysis to describe this deep, terrestrial environment. SURF provides access into a deep (down to 8100 ft below surface), iron-rich Paleoproterozoic sedimentary deposit that is plumbed by numerous sources of deeply circulating groundwater. Geochemical analyses of subsurface fluids reveal enormous geochemical diversity ranging widely in salinity, oxidation state (ORP 330 to -328 mV), and concentrations of redox sensitive species (e.g., Fe2+ from bdl to 6.2 mg/L and SS2- from 7 to 2778 µg/L). As a direct result of this compositional buffet, Gibbs energy calculations reveal there is an abundance of energy for microbial metabolism from the oxidation of sulfur, iron, nitrogen, methane, and manganese oxides. Pyrotag DNA sequencing reveals diverse communities of chemolithoautotrophs, thermophiles, both aerobic and anaerobic heterotrophs, and numerous uncultivated clades. Extrapolated across the mine footprint, these data suggest a complex spatial mosaic of subsurface primary productivity that is in good agreement with predicted energy density. Further application of this approach will significantly expand our understanding of the deep terrestrial biosphere.