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

前寒武纪盾状岩层中的深层裂缝中蕴藏着年龄从几万年的微咸流体到超过10亿年的高盐流体不等的流体。压裂液与围岩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，随着时间的推移，非含水硅酸盐在封闭系统中转变为粘土，导致高盐度。这些前寒武纪地壳深处的盐水是否开始是被困的海水，以及它们是否含有微生物群落，这些微生物群落已经适应了随着时间的推移而增加的盐度，目前还不清楚。尽管人们认为这种深埋的古盐水分布广泛，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摩阿布霍特松金矿和铀矿3公里深处发现了高盐盐水，这是NSF/ icdp支持的一个项目的一部分，该项目调查了最近发生的5.5级地震。盐水的盐度比他们之前在南非取样的任何盐水都要高10倍。盐度也超过了已知的产甲烷微生物的生长极限。含甲烷的气体、同位素数据和被困在矿物中的流体包裹体表明，这些盐水可能至少有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）的古老盐水。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，并将表征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，它们可能会拥有酶，这些酶将被证明对修复南非和其他地方矿区广泛存在的地表尾矿池中有毒金属和放射性核素污染的水有用。如果在这些裂缝中没有微生物生命，那么它们可能为研究早期地球生命构成的非生物过程提供了一个窗口。研究人员对附近矿山深部微咸裂缝水中的微生物群落进行了表征，揭示了多层共生微生物群落，这些微生物群落可以回收生物产生的CH4。嗜盐产甲烷菌和氧化甲烷菌是未知的，因此(1)其他类型的微生物C循环必须在这里盛行，或者(2)C循环仅限于非生物反应。他们成功地将封隔器/镍铬合金u型管安装到一条高度为3.2公里的高盐水充填裂缝中。还有一个钢质阀门在3千米高的地方。但是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，研究人员面临失去对世界级生物地球化学遗址进行采样的机会。因此，他们建议返回摩押霍宋矿，在南非同事的帮助下，对这些盐水进行全面调查和抽样，并采取步骤，确保今后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学、超转录组学和脂质组学分析，气体用于同位素分析和定年，水用于溶解有机碳表征，以及密封和测量其他钻孔。这些盐水样品提供的数据将测试以下假设：1)在更深、更热、高盐的压裂液中，生命受到抑制细胞内水分流失的能量成本的限制，过去数十亿年由水/岩石反应形成的非生物有机化合物清单以及生物生成的有机物质将首次出现并表征；2)低温高盐裂缝中存在的微生物群落在系统发育上与微咸裂缝水中存在的微生物群落相似，而与现有地表盐田的嗜盐菌无关；3)在微咸流体中发现的生物源性ch4支持的群落将被高盐流体中非生物源性碳氢化合物支持的群落所取代，参与渗透调节的基因表达更多，脂质成分提供较低的膜通透性。该奖项反映了美国国家科学基金会的法定使命，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.