Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.
Proc Natl Acad Sci U S A. 2014 Apr 15;111(15):5474-9. doi: 10.1073/pnas.1400643111. Epub 2014 Mar 27.
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 NH4(+) 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.
简单的烷基硫醇，如甲硫醇（CH3SH），被广泛认为在海底温泉流体中形成。生物非生物还原无机碳（CO2 或 CO）被推测为原始热液环境中原始代谢和微生物生命出现的起始反应。硫醇也是热液痕量金属的假定配体，也是相关微生物群落的潜在燃料。为了限制海底热液系统中 CH3SH 的来源和汇，我们首次确定了来自超镁铁质、镁铁质和沉积物覆盖的中洋脊环境的各种热液流体中 CH3SH 的丰度。我们的数据表明，CH3SH 的分布与无机碳的亚稳平衡不一致，表明生物非生物碳还原的产生比以前提出的更为有限。在所有未沉积系统的高温流体（>200°C）中，CH3SH 的浓度均均匀较低（10(-8) M），在许多情况下，表明与 CH4 处于亚稳平衡。然而，通过海水混合形成的相关低温流体（<200°C）与高温源流体相比，始终富含 CH3SH（高达10(-6) M）以及 NH4(+)和低分子量烃，类似于我们在沉积物中观察到的系统。这强烈暗示了上涌流体与微生物生物量或相关溶解有机物质在地下含水层中混合时的热成因相互作用。未沉积热液系统中地下有机物的广泛热降解可能是有机生产的重要来源，并可能影响较冷的近海底和羽流栖息地中微生物的代谢策略。
