Geochemical-dependent stratification of microbial chemolithoautotrophy in a high carbon dioxide subsurface aquifer

最近的研究在含水层中发现了多种多样的新生物，并提出了二氧化碳固定在深层碳循环中的意想不到的作用。具有化能自养（利用无机电子供体和受体固定二氧化碳）能力的生物的比例以及二氧化碳固定途径和活性水平随地球化学环境的变化基本上仍然未知。我建议探讨这些问题，通过分析微生物群落的含水层流体来源于不同的深度和地质构造的喷发水晶间歇泉（犹他州，美国）在四天的喷发周期。鉴于地质背景，约800米深的含水层很可能在地球化学和微生物群落组成方面都是分层的。我假设，化能自养的程度，二氧化碳固定发生的途径，和活动水平将随氧气（近地表流体）的可用性而变化，溶解亚铁，氢，甲烷，硫化氢，有机碳和二氧化碳浓度（在喷发周期中变化至少30倍）。我将使用基因组解析宏基因组和metatranscriptomic方法，结合地球化学测量，以评估社区成员的代谢潜力作为流体组成的函数。对于使用可识别的电子供体和受体的生物体，以及基于宏基因组分析预测为自养生物的生物体，我将使用同位素标记的二氧化碳微观实验来测试化能自养。该项目将提供关于地下二氧化碳固定的重要性的新信息，并深入了解作为地球化学条件函数的化能无机自养活动的种类和分布。

Recent research has detected a vast diversity of novel organisms in aquifers and suggested an unexpected role for carbon dioxide fixation in the deep carbon cycle. The fraction of organisms with the capacity for chemolithoautotrophy (carbon dioxide fixation using inorganic electron donors and acceptors) and the variation of carbon dioxide fixation pathways and activity levels with geochemical environment remain essentially unknown. I propose to explore these questions by analyzing microbial communities in aquifer fluids that are sourced from different depths and geological formations by eruption of Crystal Geyser (Utah, USA) over the four-day eruption cycle. Given the geological context, it is likely that the ~800 m-deep aquifer is stratified, both geochemically and in microbial community composition. I hypothesize that the extent of chemolithoautotrophy, the pathways by which carbon dioxide fixation occurs, and activity levels will vary with availability of oxygen (for near-surface fluids), dissolved ferrous iron, hydrogen, methane, hydrogen sulfide, organic carbon and carbon dioxide concentrations (which varies by at least 30 times over the eruption cycle). I will use genome-resolved metagenomic and metatranscriptomic methods, in combination with geochemical measurements, to evaluate the metabolic potential of community members as a function of fluid composition. For organisms that use identifiable electron donors and acceptors and that are predicted to be autotrophs based on metagenomic analysis, I will use an isotopically labeled carbon dioxide microcosm experiment to test for chemolithoautotrophy. The project will provide new information about the prominence of carbon dioxide fixation in the subsurface and insight into the variety and distribution of chemolithoautotrophic activity as a function of geochemical conditions.