Crespo-Medina Melitza, Twing Katrina I, Sánchez-Murillo Ricardo, Brazelton William J, McCollom Thomas M, Schrenk Matthew O
Center for Education, Conservation and Research, Inter-American University of Puerto RicoSan Juan, PR, United States.
Department of Biology, University of UtahSalt Lake City, UT, United States.
Front Microbiol. 2017 May 23;8:916. doi: 10.3389/fmicb.2017.00916. eCollection 2017.
Uplifted ultramafic rocks represent an important vector for the transfer of carbon and reducing power from the deep subsurface into the biosphere and potentially support microbial life through serpentinization. This process has a strong influence upon the production of hydrogen and methane, which can be subsequently consumed by microbial communities. The Santa Elena Ophiolite (SEO) on the northwestern Pacific coast of Costa Rica comprises ~250 km of ultramafic rocks and mafic associations. The climatic conditions, consisting of strongly contrasting wet and dry seasons, make the SEO a unique hydrogeological setting, where water-rock reactions are enhanced by large storm events (up to 200 mm in a single storm). Previous work on hyperalkaline spring fluids collected within the SEO has identified the presence of microorganisms potentially involved in hydrogen, methane, and methanol oxidation (such as , and spp., respectively), as well as the presence of methanogenic Archaea (such as ). Similar organisms have also been documented at other serpentinizing sites, however their functions have not been confirmed. SEO's hyperalkaline springs have elevated methane concentrations, ranging from 145 to 900 μM, in comparison to the background concentrations (<0.3 μM). The presence and potential activity of microorganisms involved in methane cycling in serpentinization-influenced fluids from different sites within the SEO were investigated using molecular, geochemical, and modeling approaches. These results were combined to elucidate the bioenergetically favorable methane production and/or oxidation reactions in this tropical serpentinizing environment. The hyperalkaline springs at SEO contain a greater proportion of Archaea and methanogens than has been detected in any terrestrial serpentinizing system. Archaea involved in methanogenesis and anaerobic methane oxidation accounted from 40 to 90% of total archaeal sequences. Genes involved in methanogenic metabolisms were detected from the metagenome of one of the alkaline springs. Methanogenic activities are likely to be facilitated by the movement of nutrients, including dissolved inorganic carbon (DIC), from surface water and their infiltration into serpentinizing groundwater. These data provide new insight into methane cycle in tropical serpentinizing environments.
隆升的超镁铁质岩石是碳和还原力从深部地下向生物圈转移的重要载体，并可能通过蛇纹石化作用支持微生物生命。这一过程对氢气和甲烷的产生有强烈影响，随后这些气体可被微生物群落消耗。位于哥斯达黎加西北太平洋海岸的圣埃琳娜蛇绿岩（SEO）由约250公里的超镁铁质岩石和镁铁质组合构成。强烈对比的干湿季节组成的气候条件，使SEO成为一个独特的水文地质环境，在那里大暴雨事件（单次暴雨可达200毫米）增强了水岩反应。先前对在SEO内采集的高碱性泉水流体的研究已确定存在可能参与氢气、甲烷和甲醇氧化的微生物（分别如 、 和 属），以及产甲烷古菌（如 属）。在其他蛇纹石化地点也记录到了类似的生物，但其功能尚未得到证实。与背景浓度（<0.3 μM）相比，SEO的高碱性泉水甲烷浓度有所升高，范围为145至900 μM。利用分子、地球化学和建模方法，研究了来自SEO内不同地点受蛇纹石化影响的流体中参与甲烷循环的微生物的存在情况和潜在活性。将这些结果结合起来，以阐明在这个热带蛇纹石化环境中生物能量学上有利的甲烷产生和/或氧化反应。SEO的高碱性泉水中古菌和产甲烷菌的比例比在任何陆地蛇纹石化系统中检测到的都要高。参与产甲烷和厌氧甲烷氧化的古菌占古菌总序列的40%至90%。从其中一个碱性泉水的宏基因组中检测到了参与产甲烷代谢的基因。包括溶解无机碳（DIC）在内的养分从地表水的移动及其渗入蛇纹石化地下水，可能促进了产甲烷活动。这些数据为热带蛇纹石化环境中的甲烷循环提供了新的见解。
