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

前寒武纪盾构岩层中的深裂缝蕴藏着流体，其年龄从几万年的微咸水流体到超过10亿年的高盐流体不等。压裂液和围岩之间的广泛反应导致氦、氢、甲烷、短链碳氢化合物、氧化剂和可能的其他化合物的产生，并随着时间的推移在封闭系统中无水硅酸盐转化为粘土而导致高盐度。这些深厚的前寒武纪地壳卤水是否开始时是被困住的海水，以及它们是否含有适应随着时间推移盐度不断上升的微生物群落，目前尚不清楚。尽管这种深层的、古老的卤水被认为是普遍存在的，但它们只在少数几个地点被用于科学研究。这些主要调查人员最近在Moab KhotSong金矿和铀矿发现了3公里深的高盐度卤水，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采集的任何样品都高出10倍。盐度也超过了产甲烷微生物的已知生长极限。含甲烷气体、同位素数据和矿物中的流体包裹体表明，卤水可能至少有20亿年的历史。这个地点在世界上是独一无二的，因为它提供了在高温(55摄氏度)下访问古代盐水的途径。研究人员将分析这些独特的地下卤水的化学成分，包括气体能源的来源和数量，他们将描述这些古老卤水中的微生物群落。如果这些裂缝中存在任何极端细菌，它们很可能会拥有一些酶，这些酶将被证明对修复地表尾矿池中被有毒金属和放射性核素污染的水很有用，这些尾矿池在南非和其他地方的矿区很普遍。如果这些裂缝中没有微生物生命，那么它们可能会提供一个窗口，让人们了解地球早期生命的构成要素的非生物过程。研究人员对附近矿山深含咸水裂隙水的微生物群落进行了表征，发现了多层共养微生物群落，这些微生物群落回收生物产生的甲烷。嗜盐产甲烷菌和甲烷菌是未知的，因此(1)其他类型的微生物C循环必须在这里占优势，或者(2)C循环仅限于非生物反应。他们成功地将封隔器/Inconel U形管安装到一个3.2kmbls的高盐水充填裂缝中。另一个是3千米的钢制阀门，但不断增加的压力和腐蚀导致这两个阀门都泄漏。随着NSF/ICDP项目结束时关键人员的损失，钻孔的坍塌，以及由于其有限的体积而造成的盐水的损失，研究人员面临着失去对世界级生物地球化学遗址进行采样的机会。因此，他们提议返回Moab KhotSong矿，并在南非同事的帮助下，对这些卤水进行全面调查和采样，并采取措施确保未来的国际研究人员能够长期使用。他们建议收集足够的生物质用于后基因组学、后基因组学和脂肪组学分析，收集足够的气体用于同位素分析和测年，收集足够的水用于描述溶解有机碳，以及密封和测量其他钻孔。这些卤水样品提供的数据将检验以下假设：1)更深、更热、高盐度裂缝流体中的生命受到对抗细胞内水分损失的能量成本的限制，数十亿年来水/岩石反应形成的非生物有机化合物以及生物生成有机质的清单将首次出现并被描述；2)存在于较冷的高盐度裂缝中的微生物群落在系统发育上与存在于微咸水中的类群相似，与现有表层盐田的嗜盐微生物无关；3)在半咸水中发现的生物来源的CH4支持的群落将被在高盐度流体中由非生物碳氢化合物支持的社区所取代，参与渗透调节的基因的更多表达以及其组成提供较低膜渗透性的脂质。这一奖项反映了NSF的法定使命，并通过使用基金会的智力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.