The origin of methanethiol in midocean ridge hydrothermal fluids
The origin of methanethiol in midocean ridge hydrothermal fluids
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DOI：
10.1073/pnas.1400643111
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发表时间：
2014-03
期刊：
影响因子：
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通讯作者：
E. Reeves;J. Mcdermott;J. Seewald
中科院分区：
文献类型：
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作者：
E. Reeves;J. Mcdermott;J. Seewald
简单的烷基硫醇，如甲烷硫醇，被广泛推测为在海底温泉流体中自发形成，并参与促进早期地球热液系统中的蛋白质代谢和微生物生命的出现，热液衍生金属的络合，以及作为微生物生态系统的燃料。现有的模型表明，甲烷乙烷是通过热液无机碳（CO2或CO）的非生物还原形成的。我们表明，甲烷乙烷是积极生产的低温混合区的热液系统，但我们的数据表明，这是热破坏的预先存在的有机物质（可能是地下微生物生物量）负责。海底下混合过程中有机硫化合物和其他降解产物的形成可能会影响微生物生活的低温热液流体的地球化学。简单的烷基硫醇，如甲烷硫醇（CH3SH），被广泛推测形成于海底温泉流体中。假定的CH3SH合成无机碳（CO2或CO）的非生物（非生物）还原已被调用作为一个起始反应的出现，在原始热液环境中的蛋白质代谢和微生物生命。硫醇也是热液微量金属的假定配体和相关微生物群落的潜在燃料。在努力限制源和汇的CH3SH在海底热液系统中，我们首次确定其丰富的各种热液流体所产生的超镁铁质，镁铁质和沉积物覆盖的Mirachian脊设置。我们的数据表明，CH3SH的分布与无机碳的亚稳平衡不一致，表明非生物碳还原的生产比以前提出的更有限。在所有未沉积系统的高温流体（> 200 ° C）中，CH3SH的浓度都很低（约10 − 8 M），在许多情况下，这表明它们与CH4处于亚稳态平衡。然而，由海水混合形成的相关低温流体（<200 ° C）总是富含CH3SH（高达10 - 6 M），沿着和相对于高温源流体的低分子量烃，类似于我们对沉积物承载系统的观察。这强烈暗示了地壳含水层地下混合过程中上涌流体与微生物生物量或相关溶解有机物之间的生热相互作用。地下有机物的广泛热降解可能是未沉积热液系统中有机物生产的一个重要来源，并可能影响较冷的近海底和羽流生境中的微生物代谢策略。
Significance Simple alkyl thiols such as methanethiol are widely speculated to spontaneously form in seafloor hot spring fluids and are implicated in facilitating the emergence of protometabolism and microbial life in early Earth hydrothermal systems, the complexation of hydrothermally derived metals, and as fuels for microbial ecosystems. Existing models suggest that methanethiol forms by nonbiological reduction of hydrothermal inorganic carbon (CO2 or CO). We demonstrate that methanethiol is actively produced in low-temperature mixing zones of hydrothermal systems, but our data suggest it is the thermal destruction of preexisting organic matter (likely subsurface microbial biomass) that is responsible. Formation of organosulfur compounds and other degradation products during subseafloor mixing may influence the biogeochemistry of low-temperature hydrothermal fluids inhabited by microbial life. Simple alkyl thiols such as methanethiol (CH3SH) are widely speculated to form in seafloor hot spring fluids. Putative CH3SH synthesis by abiotic (nonbiological) reduction of inorganic carbon (CO2 or CO) has been invoked as an initiation reaction for the emergence of protometabolism and microbial life in primordial hydrothermal settings. Thiols are also presumptive ligands for hydrothermal trace metals and potential fuels for associated microbial communities. In an effort to constrain sources and sinks of CH3SH in seafloor hydrothermal systems, we determined for the first time its abundance in diverse hydrothermal fluids emanating from ultramafic, mafic, and sediment-covered midocean ridge settings. Our data demonstrate that the distribution of CH3SH is inconsistent with metastable equilibrium with inorganic carbon, indicating that production by abiotic carbon reduction is more limited than previously proposed. CH3SH concentrations are uniformly low (∼10−8 M) in high-temperature fluids (>200 °C) from all unsedimented systems and, in many cases, suggestive of metastable equilibrium with CH4 instead. Associated low-temperature fluids (<200 °C) formed by admixing of seawater, however, are invariably enriched in CH3SH (up to ∼10−6 M) along with and low-molecular-weight hydrocarbons relative to high-temperature source fluids, resembling our observations from a sediment-hosted system. This strongly implicates thermogenic interactions between upwelling fluids and microbial biomass or associated dissolved organic matter during subsurface mixing in crustal aquifers. Widespread thermal degradation of subsurface organic matter may be an important source of organic production in unsedimented hydrothermal systems and may influence microbial metabolic strategies in cooler near-seafloor and plume habitats.