The subsurface is Earth's largest reservoir of biomass. Micro‐organisms are the dominant lifeforms in this habitat, but the nature of their in situ activities remains largely unresolved. At the Deep Mine Microbial Observatory (DeMMO) located in the Sanford Underground Research Facility (SURF) in Lead, South Dakota (USA), we performed in situ electrochemical incubations designed to assess the potential for deep groundwater microbial communities to utilize extracellular electron transfer to support microbial respiration. DeMMO 4 was chosen for its stable geochemistry and microbial community. Graphite and indium tin oxide electrodes poised at −200 mV versus SHE were incubated along with open circuit controls and various minerals in a parallel flow reactor that split access to fluids across different treatments. From the patterns of net current over time (fluctuating between anodic and cathodic currents over the course of a few days to weeks) and the catalytic features measured using periodic cyclic voltammetry, evidence of both oxidative and reductive microbe‐electrode interactions was observed. The predominant catalytic activity ranged from −210 to −120 mV. The observed temporal variability in electrochemical activity was unexpected given the documented stability in major geochemical parameters. This suggests that the accessed fluids are more heterogeneous in electrochemically active microbial populations than previously predicted from the stable community composition. As previously reported, the fracture fluid and surface‐attached microbial communities at SURF differed significantly. However, only minimal differences in community composition were observed between poised potential electrodes, open circuit electrodes, and mineral incubations. These data support that in this environment the ability to attach to surfaces is a stronger driver of microbial community structure than the type or reactivity of the surface. We demonstrate that insight into specific activities can be gained from electrochemical methods, specifically chronoamperometry coupled with routine cyclic voltammetry, which provide a sensitive approach to evaluate microbial activities in situ.

中文翻译：

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美国南达科他州深矿微生物观测站（DeMMO）的原位微生物活性的电化学证据

地下是地球上最大的生物量存储库。微生物是该栖息地的主要生命形式，但其原位活动的性质仍未得到解决。在位于美国南达科他州铅市的桑福德地下研究设施（SURF）的深层微生物观测站（DeMMO）中，我们进行了原位电化学孵育，旨在评估深层地下水微生物群落利用细胞外电子转移到支持微生物呼吸。选择DeMMO 4是因为其具有稳定的地球化学和微生物群落。将相对于SHE保持在-200 mV的石墨和铟锡氧化物电极与开路控制和各种矿物质在平行流反应器中进行孵育，该平行流反应器将通过不同处理获得的流体分开。从随着时间的净电流模式（在几天到几周的时间内阳极和阴极电流之间波动）和使用周期性循环伏安法测量的催化特性，可以观察到氧化和还原微生物-电极相互作用的证据。主要的催化活性为-210至-120 mV。鉴于已记录的主要地球化学参数的稳定性，电化学活性的时间变化是出乎意料的。这表明，与以前从稳定群落组成中预测的结果相比，在电化学活性微生物种群中进入的流体的异质性更高。如先前报道，SURF处的裂缝流体和表面附着的微生物群落有显着差异。然而，在平衡的电势电极，开路电极和矿物质孵化之间，仅观察到群落组成的最小差异。这些数据表明，在这种环境下，与表面的附着或附着能力比表面的类型或反应性更强。我们证明，可以通过电化学方法获得特定活动的见解，特别是计时安培法与常规循环伏安法相结合，这提供了一种敏感的方法来就地评估微生物活性。