Methanogens in H2-rich hydrothermal fluids resulting from phase separation in a sediment-starved, basalt-hosted hydrothermal system
Methanogens in H2-rich hydrothermal fluids resulting from phase separation in a sediment-starved, basalt-hosted hydrothermal system
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DOI：
10.1016/j.chemgeo.2016.11.004
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发表时间：
2016-12
期刊：
影响因子：
3.9
通讯作者：
T. Toki;Arito Hamamoto;Miki Tawata;J. Miyazaki;Kentaro Nakamura;Mariko Abe;K. Takai;Y. Sano;N. Takahata;U. Tsunogai;J. Ishibashi
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文献类型：
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作者：
T. Toki;Arito Hamamoto;Miki Tawata;J. Miyazaki;Kentaro Nakamura;Mariko Abe;K. Takai;Y. Sano;N. Takahata;U. Tsunogai;J. Ishibashi
我们在这里报道了在南马里亚纳弧后扩张中心太古代热液遗址观察到的特殊化学和微生物组成，它产生了两种截然不同的热液。一种是340℃下含低浓度甲烷的黑烟热液，具有相对较高的碳同位素比值(δ13C)，−7.8‰，表明甲烷来自岩浆源区；因此，这是一种相当普通的玄武岩容矿热液活动。相比之下，另一种流体是117C下的清澈的烟雾状热液，含有高浓度的甲烷，碳同位素比率非常低(−49.7‰)。太古代热液场所的寄主岩石是玄武岩，因此，地幔岩石蛇纹岩作用所产生的费托反应不可能作为甲烷中“轻”碳的来源。此外，二氧化碳的碳同位素比值表明，二氧化碳和甲烷的来源不是有机物质。剩余的可能性是生物甲烷，通过从覆盖着清澈的烟雾热液喷口的两块岩石和原位培养系统中培养出高度嗜热的氢氧化甲烷菌而得到证实。尽管该生态系统中产甲烷菌的优势度和丰度都很低，但其数量与氢浓度与产甲烷菌丰度之间的关系是一致的(Takai等人，2015年)。这些结果表明，在蛇纹石和玄武岩赋存的热液系统中，相分离导致了氢的聚集和随后的高温地下岩石自养微生物生态系统的持续存在。这种类型的生态系统可能出现在现代地球上其他地方的类似环境中；此外，在地质历史上，类似的群落可能存在于其他类型的深海热液系统中。
We here report on specific chemical and microbial compositions observed at the Archaean hydrothermal site in the Southern Mariana backarc spreading center, which produces two remarkably different hydrothermal fluids. One was black smoker hydrothermal fluid at 340 °C containing a low concentration of methane with a relatively high carbon isotope ratio (δ13C of methane relative to VPDB), −7.8‰, indicating that methane originated from a magmatic source; thus, this is a fairly ordinary hydrothermal fluid for basalt-hosted hydrothermal activity. In contrast, the other fluid was clear smoker hydrothermal fluid at 117 °C containing a high concentration of methane with a very low carbon isotope ratio (−49.7‰). The host rock of the Archaean hydrothermal site is basalt, and therefore Fischer-Tropsch-type reactions resulting from serpentinization of mantle rocks are not feasible as a source for the “light” carbon in methane. Additionally, the carbon isotope ratio of carbon dioxide demonstrated that the sources of CO2and CH4were not organic materials. The remaining possibility, biogenic methane, was confirmed by cultivation of hyperthermophilic hydrogen-oxidizing methanogens from both rocks covering the vent of clear smoker hydrothermal fluids and in situ cultivation systems. Although the dominance and abundance of methanogens were very low in this ecosystem, the number was consistent with the relationship between hydrogen concentration and methanogen abundance (Takai et al., 2015). These results suggest that phase separation led to concentration of hydrogen and subsequent persistence of a hyperthermophilic subsurface lithoautotrophic microbial ecosystem in both serpentine-hosted and basalt-hosted hydrothermal systems. This type of ecosystem may occur in similar settings elsewhere on modern earth; in addition, similar communities may have existed in other types of deep-sea hydrothermal systems in the geological past.