RAPID: Collaborative Research: Carbon Cycling in Subsurface Hypersaline Environments Near the Abiotic Fringe

前寒武纪盾岩层中的深裂缝容纳的流体的年龄范围从数万年的半咸水流体到超过十亿年的超咸水流体。压裂液和周围岩石之间的广泛反应导致氦、氢、甲烷、短链烃、氧化剂和可能的其他化合物的产生，并且随着时间的推移，由于非含水硅酸盐在封闭系统中变成粘土，导致高盐度。这些前寒武纪地壳深处的盐水是否起源于被困的海水，以及它们是否含有随着时间的推移而适应盐度增加的微生物群落，目前尚不清楚。虽然这种深层的古代盐水被认为是广泛存在的，但它们只在少数几个地方被用于科学研究。这些主要研究人员最近在Moab Khotsong金矿和铀矿3公里深处发现了高盐卤水，这是NSF/ICDP支持的调查最近5.5级地震的项目的一部分。盐水的盐度是他们以前在南非取样的盐水的10倍。盐度也超过了产甲烷微生物的已知生长极限。含甲烷的气体、同位素数据和矿物中的流体包裹体表明，盐水可能至少有20亿年的历史。这个地方在世界上是独一无二的，因为它提供了高温（55摄氏度）的古盐水。研究人员将分析这些独特的地下盐水的化学成分，包括气体能源的来源和数量，并描述这些古老盐水中的微生物群落。如果这些裂缝中存在任何极端微生物，它们可能拥有酶，这些酶将被证明可用于修复南非矿区和其他地方广泛分布的地表尾矿池中的有毒金属和放射性核素污染的水。如果在这些裂缝中没有微生物生命，那么它们可能提供了一个窗口，让我们了解早期地球生命的构建过程。研究人员已经对附近矿井深咸裂隙水的微生物群落进行了表征，揭示了多层次互养微生物群落，它们回收生物产生的CH 4。 嗜盐产甲烷菌和甲烷氧化菌是未知的，因此（1）其他类型的微生物碳循环必须占主导地位，或者（2）碳循环仅限于非生物反应。他们成功地将封隔器/因科镍合金U形管安装到一个3.2 kmbls的高盐盐水填充裂缝中。另一个在3公里处有一个钢阀门，但不断增加的压力和腐蚀导致了两者的泄漏随着NSF/ICDP项目结束时关键人员的流失、钻孔的坍塌以及有限体积的盐水的流失，研究人员面临着失去对世界级地球化学场地进行采样的机会。因此，他们建议返回莫阿布霍特松矿，在南非同事的帮助下，对这些盐水进行全面调查和取样，并采取步骤，确保今后的国际研究人员能够长期进入。他们建议收集足够的生物量用于宏基因组、元转录组和脂质组分析，收集气体用于同位素分析和测年，收集水用于溶解有机碳表征，以及密封和安装其他钻孔。由这些盐水样品提供的数据将测试以下假设：1）在更深、更热、高盐压裂液中的生命受到对抗细胞内水损失的能量成本的限制，并且在过去数十亿年中由水/岩石反应形成的非生物有机化合物以及生物产生的有机物质的清单将首次存在并表征; 2）存在于较冷的高盐度裂缝中的微生物群落在遗传学上与存在于微咸水裂缝水中的门相似，并且与现有表面盐田的嗜盐菌无关;和3）在微咸流体中发现的生物源CH 4-支持的群落将被高盐流体中的非生物源烃支持的群落所取代，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Deep fractures within Precambrian Shield rock formations host fluids that range in age from tens of thousands of years for brackish fluid to more than a billion years for hypersaline fluids. Extensive reactions between the fracture fluid and surrounding rock lead to the production of helium, hydrogen, methane, short-chain hydrocarbons, oxidants and likely other compounds and to hypersalinity as non-hydrous silicates alter to clay in closed systems over time. Whether these deep Precambrian crust brines began as trapped ocean water and whether they contain microbial communities that have adapted to the increasing salinity over time is not known. Although such deep-seated, ancient brines are believed to be widespread, they have only been accessed in a few locations for scientific study. These principal investigators recently discovered hypersaline brines at 3 km depth in Moab Khotsong gold and uranium mine as part of an NSF/ICDP-supported project investigating a recent magnitude 5.5 earthquake. The brine salinity is 10x greater than any they have previously sampled in South Africa. Salinity also exceeds the known growth limit for methane-producing microbes. The methane-bearing gas, isotopic data, and fluid inclusions trapped in minerals suggest the brine could be at least 2 billion years old. This site is unique in the world in that it provides access to an ancient brine at high temperature (55 degree Centigrade). Researchers will analyze the chemistry of these unique subsurface brines, including the sources and amounts of gaseous energy sources and they will characterize the microbial communities in these ancient brines. If any extremophiles exist in these fractures, they will likely possess enzymes that will prove useful for remediating toxic metal- and radionuclide-contaminated water in the surface tailings ponds that are widespread in the mining districts of South Africa and elsewhere. If microbial life is absent in these fractures then they may provide a window into the abiotic processes responsible for the building blocks of life in the early Earth. The investigators have characterized the microbial communities of deep brackish fracture water at nearby mines, which have revealed multi-tier syntrophic microbial communities that recycle biogenically produced CH4. Halophilic methanogens and methanotrophs are not known and so either (1) other types of microbial C cycling must prevail here or (2) C cycling is limited to abiotic reactions. They successfully installed a packer/inconel U-tube into one hypersaline brine-filled fracture at 3.2 kmbls. and a steel valve on another at 3 kmbls., but increasing pressure and corrosion are causing both to leak. With the loss of key personnel at the end of the NSF/ICDP project, the collapse of the boreholes, and the loss of brine given their finite volume, researchers face losing an opportunity to sample a world class biogeochemical site. They therefore propose to return to Moab Khotsong Mine and with help from their South African colleagues to undertake a comprehensive survey and sampling of these brines and to take steps to secure longer-term access for future international researchers. They propose collecting sufficient biomass for metagenomic, metatranscriptomic and lipidomic analyses, gas for isotopic analyses and dating, and water for dissolved organic carbon characterization, as well as sealing and instrumenting other boreholes. The data provided by these brine samples will test the following hypotheses: 1) Life in the deeper, hotter, hypersaline fracture fluids is constrained by the energetic cost of combating intracellular water loss and an inventory of abiotic organic compounds formed by water/rock reactions over the past billions of years as well as biologically generated organic matter will be present and characterized for the first time; 2) Microbial communities present in cooler hypersaline fractures will be phylogenetically similar to phyla present in brackish fracture water and not related to the halophiles of existing surface saltpans; and 3) Biogenic CH4-supported communities found in brackish fluids will be replaced by communities supported by abiogenic hydrocarbons in hypersaline fluids, with greater expression of genes involved in osmotic regulation and with lipids whose composition provide lower membrane permeability.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.