Serpentinization involves the hydration and alteration of ultramafic rocks, which produces hydrogen (H₂) and methane (CH₄) and results in distinctive groundwater chemistries. As reacted fluids mix with recharging surface water, gradients in chemistry and microbiology develop in the subsurface. We present a comprehensive analysis of biogeochemical gradients in the water column of a serpentinite-hosted well, CSW1.1, at the Coast Range Ophiolite Microbial Observatory (CROMO) in California, USA. Samples for geochemistry, 16S rRNA gene sequencing, and metagenomics were collected at four discrete depths from the top of the well corresponding to 100%, 50%, 15%, and 0% of atmospheric oxygen (O₂) levels, and from the well base at 19.5 m depth. Gibbs energy calculations assessed the energy available for a suite of reactions coupled to O₂, sulfate (SO₄²⁻), and nitrate (NO₃⁻). Metagenomic data from the profile was used to construct metagenome assembled genomes (MAGs) to evaluate the completeness of biochemical pathways and compare the relative abundance of key diagnostic genes. Bioenergetic data point to the favorability of CH₄ oxidation reactions despite little genetic evidence for this. Amplicon sequencing results highlight the abundance of key taxa affiliated with the genera Truepera, Serpentinomonas, and Dethiobacter. Although concentrations of NO₃⁻ and H₂ are low, genes for NO₃⁻ reduction and oxidation of H₂ and carbon monoxide (CO) were found in high abundance. Conceptual modeling results demonstrate the net depletion of H₂ and CO in the groundwater, the consumption of CO₂ and O₂, and the potential for CH₄ emission into the atmosphere at this terrestrial site of serpentinization.

中文翻译：

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受蛇纹石化影响的含水层中的生物地球化学梯度：对地下和大气之间气体交换的影响

蛇纹石化涉及超基性岩的水化和蚀变，产生氢气 (H ₂ ) 和甲烷 (CH ₄ )，并产生独特的地下水化学成分。随着反应流体与补充地表水混合，化学和微生物学的梯度在地下发展。我们对美国加利福尼亚州海岸山脉蛇绿岩微生物观测站 (CROMO) 的蛇纹岩井 CSW1.1 的水柱中的生物地球化学梯度进行了全面分析。地球化学、16S rRNA 基因测序和宏基因组学样本在井顶四个离散深度收集，对应于 100%、50%、15% 和 0% 的大气氧 (O ₂) 水平，并从井底 19.5 m 深度。Gibbs 能量计算评估了与 O ₂、硫酸盐 (SO ₄ ^2- ) 和硝酸盐 (NO ₃ ^- )耦合的一系列反应的可用能量。来自配置文件的宏基因组数据用于构建宏基因组组装基因组 (MAG)，以评估生化途径的完整性并比较关键诊断基因的相对丰度。尽管很少有遗传证据，但生物能数据表明 CH ₄氧化反应是有利的。扩增子测序结果突出了与Truepera、Serpentinomonas和Dethiobacter属相关的关键分类群的丰度. 尽管NO ₃ ^-和H _{2 的}浓度低，但大量发现了用于NO ₃ ^-还原和氧化H ₂和一氧化碳(CO)的基因。概念建模结果证明了地下水中 H ₂和 CO的净消耗、CO ₂和 O ₂的消耗，以及在这个蛇纹石化的陆地地点向大气中排放CH ₄的潜力。