Evolution of Hydrogen-Based Microbial Communities in Deep Hydrothermal Aquifers

爱达荷州蛇河平原下的热液系统提供了一个直接观察深层地下热液系统中微生物群落如何随时间变化的机会。 蛇河平原是随着北美板块向西移动越过黄石热点而形成的，产生了一系列时间海侵的火山场和相关的热液系统，其年龄范围从200万年（Ma）的黄石火山场到16.1 Ma的麦克德米特火山场。 最近的研究表明，在Lidy温泉，与6.6马海瑟火山场的主要自养，氢为基础的微生物群落的存在。 初步研究表明，与蛇河平原上的老火山区有关的泉水沃茨中存在异养微生物。 建议系统地描述爱达荷州蛇河平原下逐渐变老的热液系统的微生物生态学和有机地球化学的变化。 了解地下热液系统中的自养氢基微生物群落如何随时间变化，并了解春季沃茨中有机物的反应性和组成的相应变化，可以深入了解早期地球上生命的进展。 具体而言，将确定泉水沃茨中存在的微生物和细菌的相对比例，并使用对适当的系统发育或功能基因具有特异性的引物组，通过定量PCR评估能够进行特定类型的异养代谢（即硫酸盐、铁和硝酸盐还原）的细菌的比例。 与此同时，将记录春季沃茨中溶解有机物（DOM）的化学和同位素组成，以评估底物生物利用度的变化，并确定该材料如何反映居民微生物群落的组成。 从自养到异养微生物群落的明显过渡提供了一个机会，以调查特定的生物过程中的DOM的成岩作用和生产的难降解有机物，保存在环境中的作用。 这些数据将用于描述在大约一千万年的时间范围内深层热液系统的变化和生态进展。

The hydrothermal systems underlying the Snake River plain in Idaho present an opportunity to directly observe how microbial communities in deep subsurface hydrothermal systems change over time. The Snake River plain was formed as the North American plate has moved west over the Yellowstone Hotspot producing a time-transgressive series of volcanic fields and associated hydrothermal systems that range in age from the 2.0 million year old (Ma) Yellowstone volcanic field to the 16.1 Ma McDermitt volcanic field. Recent studies show the presence of a predominantly autotrophic, hydrogen-based microbial community at Lidy Hot Spring, associated with the 6.6 Ma Heise volcanic field. Preliminary studies suggest the presence of heterotrophic microorganisms in spring waters associated with older volcanic fields on the Snake River plain. It is proposed to systematically characterize changes in the microbial ecology and organic geochemistry of progressively older hydrothermal systems underlying the Snake River plain of Idaho. Understanding how autotrophic, hydrogen-based microbial communities in subsurface hydrothermal systems change over time, and understanding the accompanying changes in the reactivity and composition of organic matter in spring waters could yield insight to understanding the progression of life on the early Earth. Specifically, the relative proportion of Archaea and Bacteria present in spring waters will be determined, and the proportion of Bacteria capable of specific types of heterotrophic metabolism (i.e. sulfate-, iron- and nitrate reduction) will be assessed with quantitative PCR using primer sets specific for appropriate phylogenetic or functional genes. Parallel to this effort, the chemical and isotopic composition of dissolved organic matter (DOM) in the spring waters will be documented to assess changes in the bioavailability of substrates and to determine how this material reflects the composition of the resident microflora. The apparent transition from autotrophic to heterotrophic microbial communities provides an opportunity to investigate the roles of specific biological processes in the diagenesis of DOM and the production of refractory organic matter that is preserved in the environment. These data will be used to describe the variability and ecological progression of deep hydrothermal systems over a timeframe of approximately ten million years.