Using Cathodic Poised Potential Experiments to Investigate Extracellular Electron Transport in the Crustal Deep Biosphere of North Pond, Mid-Atlantic Ridge
Using Cathodic Poised Potential Experiments to Investigate Extracellular Electron Transport in the Crustal Deep Biosphere of North Pond, Mid-Atlantic Ridge
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DOI：
10.3389/fenvs.2020.00011
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发表时间：
2020-02
期刊：
影响因子：
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通讯作者：
Rose M. Jones;T. D’Angelo;B. Orcutt
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文献类型：
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作者：
Rose M. Jones;T. D’Angelo;B. Orcutt
地壳海底下覆盖了地球表面的很大一部分，但对生命栖息地的了解很少。目前还不清楚是什么代谢支持已经观察到的微观细胞，以及它们如何在资源限制下生存。由于地壳深部次表层占地球表面的很大一部分，因此微生物介导的反应可能是地球化学循环的重要贡献者。在本研究中，我们使用电化学技术来调查地壳地下微生物类群可以利用固体岩石基质（玄武岩等）的可能性。作为通过细胞外电子转移（EET）进行氧化还原反应的电子源。次表层地壳流体和矿物殖民实验中大西洋中脊西侧的北池站点的凉爽和氧玄武质地壳次表层被用作阴极平衡电位实验中的接种体。氧化微生物燃料电池（MFC）中的电极与标准氢电极相比保持在-200 mV，以模拟在相当于铁氧化的能量范围内的电子传递。以这种方式，使用固体矿物质中的还原铁作为能量的微生物从一般群落中选择到电极表面上，用于询问EET活性，并通过扫描电子显微镜（SEM）和DNA测序进行潜在鉴定。结果表明，在该地点的低生物量地壳地下存在阴极EET能力的微生物群。实验中当前世代的模式表明，这些微生物群体是活跃的，但在实验的低资源条件下可能不会生长，这与其他关于深层生物圈中活动与生长的研究一致。缺乏增长阻碍了试图确定EET能力的微生物群体从这个栖息地的繁殖，但结果表明，这些微生物群体是整个地壳深部生物圈群落的一小部分。这是首次使用电微生物学技术来研究地壳深部生物圈中微生物代谢潜力的演示，揭示了研究地壳深部生物圈中EET的挑战和机遇。
The crustal sub-seafloor covers a large portion of the Earth’s surface but is poorly understood as a habitat for life. It is unclear what metabolisms support the microscopic cells that have been observed, and how they survive under resource limitation. As the deep crustal subsurface represents a significant portion of the Earth’s surface, microbially mediated reactions may therefore be significant contributors to biogeochemical cycling. In the present study, we used electrochemical techniques to investigate the possibility that crustal subsurface microbial groups can use the solid rock matrix (basalts, etc.) as a source of electrons for redox reactions via extracellular electron transfer (EET). Subsurface crustal fluids and mineral colonization experiments from the cool and oxic basaltic crustal subsurface at the North Pond site on the western flank of the Mid-Atlantic Ridge were used as inocula in cathodic poised potential experiments. Electrodes in oxic microbial fuel cells (MFCs) were poised at −200 mV versus a standard hydrogen electrode to mimic the delivery of electrons in an energy range equivalent to iron oxidation. In this way, microbes that use reduced iron in solid minerals for energy were selected for from the general community onto the electrode surface for interrogation of EET activity, and potential identification by scanning electron microscopy (SEM) and DNA sequencing. The results document that there are cathodic EET-capable microbial groups in the low biomass crustal subsurface at this site. The patterns of current generation in the experiments indicate that these microbial groups are active but likely not growing under the low-resource condition of the experiments, consistent with other studies of activity versus growth in the deep biosphere. Lack of growth stymied attempts to determine the phylogeny of EET-capable microbial groups from this habitat, but the results indicate that these microbial groups are a small part of the overall crustal deep biosphere community. This first demonstration of using electromicrobiology techniques to investigate microbial metabolic potential in the crustal deep biosphere reveals the challenges and opportunities for studying EET in the crustal deep biosphere.