Collaborative Research: Biogeochemical Processes in a Subsurface Hypersaline Environment near the Abiotic Fringe

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Deep groundwater environments contain a significant portion of Earth's biomass and the organisms therein participate in biogeochemical cycling of carbon and other elements. They are also among the candidate environments for the origin of life, i.e., for the transition from simple, abiotic chemical reactions to cellular, metabolic, replicants. This project is focused on deep (3km), ancient (1-2 billion-year-old), hypersaline fracture water, accessed via boreholes in a South African gold mine. Water-rock interactions in this system contribute to increased fluid salinity and generate hydrogen gas, methane, other short-chain hydrocarbons, and simple carbon-sulfur compounds that may be important precursors to life. This project will advance understanding of carbon cycling, saline groundwater (directly relevant to petroleum reservoirs), and the origin and early evolution of life on Earth. The project involves international collaboration and will engage both graduate and undergraduate students, with emphasis on recruiting minority/underrepresented groups.The goal of this project is to understand the interactions of abiotic and biotic processes occurring over a ~2-billion-year time scale in deep hypersaline fracture fluid environments. An initial suite of samples was collected from each of two brine boreholes. Further sampling will be conducted. Characterization of the samples will include identification and quantification of dissolved and volatile organic carbon compounds, stable isotopic analyses of inorganic and organic compounds and of fracture minerals, and radiometric dating of dissolved noble gases. On the biomass of at least one borehole, metagenomic, metatranscriptomic, metaproteomic, and lipidomic analyses, in addition to virome characterization, will be performed. The following hypotheses will be tested: 1) In the deeper, hotter (55°C) borehole where the biomass abundance is extremely low, an inventory of abiotic organic compounds formed by water-rock reactions over the past billions of years will be characterized for the first time; 2) In the shallower, cooler (48°C) borehole where the biomass abundance appears greater, the community will be supported by abiogenic hydrocarbons, exhibit a greater expression of osmotic regulation and phosphorous uptake genes, and possess lipids whose composition provide lower membrane permeability. This proposal's focus on the abiotic organic geochemistry and microbial cycling in hypersaline, hydrologically isolated, deep fracture fluids has direct applications to globally significant Precambrian hydrologic reservoirs, biodegradation of petroleum deposits, the origins and evolution of life in the subsurface, and the exploration for extant life on Mars and other planetary bodies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.