Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, USA.
Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
Sci Total Environ. 2022 Aug 25;836:155492. doi: 10.1016/j.scitotenv.2022.155492. Epub 2022 Apr 25.
Ney Springs, a continental serpentinizing spring in northern California, has an exceptionally high reported pH (12.4) for a naturally occurring water source. With high conductivity fluids, it is geochemically more akin to marine serpentinizing systems than other terrestrial locations. Our geochemical analyses also revealed high sulfide concentrations (544 mg/L) and methane emissions (83% volume gas content) relative to other serpentinizing systems. Thermodynamic calculations were used to investigate the potential for substrates resulting from serpentinization to fuel microbial life, and were found to support the energetic feasibility of sulfate reduction, anaerobic methane oxidation, denitrification, and anaerobic sulfide oxidation within this system. Assessment of the microbial community via 16S rRNA taxonomic gene surveys and metagenome sequencing revealed a community composition dominated by poorly characterized members of the Izemoplasmatales and Clostridiales. The genomes of these dominant taxa point to a fermentative lifestyle, though other highly complete (>90%) metagenome assembled genomes support the potential for organisms to perform sulfate reduction, sulfur disproportionation and/or sulfur oxidation (aerobic and anaerobic). Two chemolithoheterotrophs identified in the metagenome, a Halomonas sp. and a Rhodobacteraceae sp., were isolated and shown to oxidize thiosulfate and were capable of growth in conditions up to pH 12.4. Despite being characteristic products of serpentinization reactions, little evidence was seen for hydrogen and methane utilization in the Ney Springs microbial community. Hydrogen is not highly abundant and could be consumed prior to reaching the spring community. Other metabolic strategies may be outcompeted by more energetically favorable heterotrophic or fermentation reactions, or even inhibited by other compounds in the spring such as ammonia. The unique geochemistry of Ney Springs provides an opportunity to study how local geology interacts with serpentinized fluids, while its microbial community can better inform us of the metabolic strategies employed in hyperalkaline environments.
美国加利福尼亚州北部的奈泉是一处大陆蛇纹石化泉，其水源的自然 pH 值（12.4）异常高。奈泉的导电性流体与其他陆地蛇纹石化区相比，更类似于海洋蛇纹石化系统。我们的地球化学分析还表明，与其他蛇纹石化系统相比，奈泉具有较高的硫化物浓度（544mg/L）和甲烷排放量（83%体积气体含量）。热力学计算用于研究蛇纹石化产生的底物为微生物生命供能的潜力，结果表明该系统中硫酸盐还原、厌氧甲烷氧化、反硝化和厌氧硫化物氧化等过程在能量上是可行的。通过 16S rRNA 分类基因调查和宏基因组测序对微生物群落进行评估，结果表明该群落主要由 Izemoplasmatales 和 Clostridiales 中特征描述较差的成员组成。这些优势类群的基因组表明其具有发酵生活方式，尽管其他高度完整（>90%）的宏基因组组装基因组支持硫酸盐还原、硫歧化和/或硫氧化（好氧和厌氧）的可能性。宏基因组中鉴定出的两种化能异养菌，一种是盐单胞菌属（Halomonas sp.），另一种是红杆菌科（Rhodobacteraceae sp.），它们被证明能够氧化硫代硫酸盐，并能在 pH 值高达 12.4 的条件下生长。尽管氢气和甲烷是蛇纹石化反应的特征产物，但在奈泉微生物群落中几乎没有发现它们被利用的证据。氢气并不高度丰富，可能在到达泉区群落之前就被消耗掉了。其他代谢策略可能会被更有利的异养或发酵反应所取代，甚至可能会被泉水中的其他化合物（如氨）所抑制。奈泉独特的地球化学性质为研究局部地质与蛇纹石化流体的相互作用提供了机会，而其微生物群落则可以更好地告诉我们在高碱性环境中使用的代谢策略。
