10:45 AM - 11:07 AM
[BCG07-05] The Deep Subsurface Biosphere: DSEIS and PROTEA Projects
★Invited Papers
Keywords:The Witwatersrand Basin, South Africa, ICDP-DSEIS project, PROTEAproject, Ancient, hypersaline brine
Studies over the past 35 years have demonstrated that the Earth’s biosphere extends deep beneath the surface and that the microbes inhabiting the subsurface comprise a significant proportion of the Earth’s total biomass. An estimated 2 to 6 x 1029 bacterial and archaeal cells exist in the subsurface. The depth limit is controlled in part by temperature, with habitable conditions occurring to several km at sites with low geothermal gradients. Diversity is high as well, with an estimated 1012 microbial species existing globally in the continental subsurface. Microbes in the shallow subsurface are fueled mainly by organic C derived from photosynthesis whereas microbial activities at depth are fueled primarily by H2 generated by rock-water interactions as well as by short-chain hydrocarbons generated by Fischer-Tropsch-type reactions.
The Witwatersrand Basin in South Africa has been an especially valuable study area. Mining companies drill into pristine rock, intersecting fractures containing fluids that can be analyzed for geochemistry and microbiology. Discoveries include novel taxa living in anoxic (to microoxic), anaerobic ecosystems in hydrogeologic isolation from the surface, chemoautotrophic ecosystems fueled by radiolytic H2, a single-species ecosystem of sulfate reducers (Candidatus Desulforudis audaxviator), and metabolically syntrophic communities. The DSEIS (Drilling into seismogenic zones of M2.0-M5.5 earthquakes in deep South African gold mines) project drilled to a depth of 3.2 km in Moab Khotsong Mine in South Africa primarily to study the sources of earthquakes in the region, but it also fortuitously discovered ancient (1.2 Ga), hypersaline (24 wt/% Na-Ca-Cl), moderately thermal (54 °C) brine that is of interest biogeochemically. The brine contains radiolytically generated H2, short-chain hydrocarbons, and radiolytically reworked ancient (2.9 Ga) kerogen as potential energy sources for microbes. Microbial abundance is low (~102 cells/ml) but single cell amplified genomes (SAGs) indicate the potential for active oxidation of N and S species and for denitrification, as well as compatible solute synthesis.
The PROTEA (Probing the heart of an earthquake and life in the deep subsurface) project proposes to further drill the fault zone at Moab Khotsong, providing expanded access to the hypersaline brine and enabling a tighter integration of geophysical and biogeochemical scientific aims. Hypotheses to be tested include: 1. Microbial communities in the brine actively cycle C, N, and S via microbially mediated redox reactions, 2. Alkyl thiols are abiotically generated in part by radiolytic reactions, 3. The energetic stress imposed by salinity and heat favors catabolic metabolisms with high energy yields and selects against low energy-yielding pathways, and 4. Earthquakes stimulate microbial activities through release of energy-rich gases such as H2 and CH4.
The Witwatersrand Basin in South Africa has been an especially valuable study area. Mining companies drill into pristine rock, intersecting fractures containing fluids that can be analyzed for geochemistry and microbiology. Discoveries include novel taxa living in anoxic (to microoxic), anaerobic ecosystems in hydrogeologic isolation from the surface, chemoautotrophic ecosystems fueled by radiolytic H2, a single-species ecosystem of sulfate reducers (Candidatus Desulforudis audaxviator), and metabolically syntrophic communities. The DSEIS (Drilling into seismogenic zones of M2.0-M5.5 earthquakes in deep South African gold mines) project drilled to a depth of 3.2 km in Moab Khotsong Mine in South Africa primarily to study the sources of earthquakes in the region, but it also fortuitously discovered ancient (1.2 Ga), hypersaline (24 wt/% Na-Ca-Cl), moderately thermal (54 °C) brine that is of interest biogeochemically. The brine contains radiolytically generated H2, short-chain hydrocarbons, and radiolytically reworked ancient (2.9 Ga) kerogen as potential energy sources for microbes. Microbial abundance is low (~102 cells/ml) but single cell amplified genomes (SAGs) indicate the potential for active oxidation of N and S species and for denitrification, as well as compatible solute synthesis.
The PROTEA (Probing the heart of an earthquake and life in the deep subsurface) project proposes to further drill the fault zone at Moab Khotsong, providing expanded access to the hypersaline brine and enabling a tighter integration of geophysical and biogeochemical scientific aims. Hypotheses to be tested include: 1. Microbial communities in the brine actively cycle C, N, and S via microbially mediated redox reactions, 2. Alkyl thiols are abiotically generated in part by radiolytic reactions, 3. The energetic stress imposed by salinity and heat favors catabolic metabolisms with high energy yields and selects against low energy-yielding pathways, and 4. Earthquakes stimulate microbial activities through release of energy-rich gases such as H2 and CH4.