DCO Project Summary

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Project Title
South African Terrestrial Deep Subsurface
Start DateEnd Date
2012-01-01 2013-12-31
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Recent studies of the continental subsurface microbial ecosystem present in the Witwatersrand Basin, South Africa have shown that with increasing depth and fracture water age and salinity, biogenic methane diminishes and abiogenic hydrocarbons and H2 increase and the concentration of planktonic cells slowly declines. Similarly, studies of the 16S rRNA gene in the planktonic community revealed a decrease in the relative abundance of methanogens and an increase in the relative abundance of low G+C Firmicutes with increasing depth.   Metagenome analyses of one member of this Firmicutes community, D. Audaxviator, indicated that it was capable of both heterotrophic and chemoautotrophic activity. An in situ incubation experiment suggests that some Firmicutes are acetogens that may support the aceticlastic methanogens.

Our geochemical and isotopic analyses indicate that abiogenic hydrocarbons are not utilized by the microbial community. Instead, a chemoautotrophic ecosystem is sustained by radiolytic generation of H2 and oxidants. Abiogenic hydrocarbon gases and elevated H2 have also been reported from the Canadian and Fennoscandian Precambrian shields and from ocean floor vents. The subsurface ecosystem present in the Witwatersrand Basin, therefore, is potentially wide spread in both the continental and marine crust, yet quite distinct from continental sedimentary basins or coastal margin sea floor sediments where degradation of photosynthetically produced organic matter deposited within the strata is believed to limit the extent of the subsurface microbial ecosystem. Alternatively, organic acids, thermogenically produced ~2 by ago from the thin shale layers present in the Witwatersrand Basin, could be sustaining the microbial community observed today.

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  • The Mass of Microbes in Deep African Mines Lead Lives of Quiet Desperation - submitted on ,

    Update Details:

    The Witwatersrand Basin in southern Africa, one of the oldest geological formations on Earth, began as a shallow sea about 3 billion years ago. The Basin is home to extensive gold and diamond mining operations, where humans have dug some of the deepest mines in the world. These deep mines have been a boon to scientists as well. The mining companies drill boreholes into surrounding pristine rock, which intersect with fractures filled with groundwater. Scientists can analyze this water to probe the limits of deep life and to learn how microbes make a living when trapped kilometers beneath the surface.

    DCO Deep Energy and Deep Life Community members Thomas Kieft (New Mexico Institute of Mining and Technology, USA), Verena Heuer (University of Bremen, Germany), Esta van Heerden (University of the Free State, South Africa), Barbara Sherwood Lollar (University of Toronto, Canada), and Maggie C.Y. Lau and Tullis Onstott (both at Princeton University, USA) investigated the organic matter in fracture waters to find clues to how microbes live in these ancient rocks. The researchers sampled from mine boreholes reaching just over 3.4 kilometers deep and characterized the dissolved organic matter within. Their results paint a picture of isolated microbial communities eking out a living using dissolved hydrogen gas (H2) and inorganic carbon released by the rocks, with little or no input of organic carbon from the surface. The researchers report their findings in a new paper in the journal Organic Geochemistry.

    Read more here.
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