Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, USA.
Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA.
Geobiology. 2021 Mar;19(2):173-188. doi: 10.1111/gbi.12420. Epub 2020 Nov 14.
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.
地下是地球最大的生物质储量。微生物是该栖息地的主要生命形式，但它们在原位的活动性质在很大程度上仍未得到解决。在美国南达科他州莱德的桑福德地下研究设施 (SURF) 中，我们进行了现场电化学孵育实验，旨在评估深部地下水微生物群落利用细胞外电子转移来支持微生物呼吸的潜力。DeMMO 4 因其稳定的地球化学和微生物群落而被选中。石墨和氧化铟锡电极在相对于 SHE 的 -200 mV 下被孵育，同时进行开路对照和各种矿物的平行流反应器孵育，该反应器将流体进入不同处理的通道分开。从随时间变化的净电流模式（在几天到几周的时间内，在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征来看，观察到了氧化和还原微生物-电极相互作用的证据。主要的催化活性范围从-210 到-120 mV。考虑到主要地球化学参数的记录稳定性，电化学活性的观察到的时间变异性是出乎意料的。这表明与从稳定群落组成预测的相比，访问的流体在电化学活性微生物种群中具有更大的异质性。如前所述，SURF 的裂缝流体和表面附着的微生物群落有很大的不同。然而，在 poised potential 电极、开路电极和矿物孵育之间，仅观察到群落组成的最小差异。这些数据支持在这种环境中，附着到表面的能力是微生物群落结构的更强驱动力，而不是表面的类型或反应性。我们证明，电化学方法，特别是与常规循环伏安法结合的计时安培法，可以深入了解特定的活性，为原位评估微生物活性提供了一种敏感的方法。
