Evolution of Hydrogen-Based Microbial Communities in Deep Hydrothermal Aquifers

爱达荷州斯内克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。斯内克河平原的形成是由于北美板块在黄石热点上向西移动，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温泉存在一个以自养为主的氢基微生物群落，与6.6 Ma Heise火山场有关。初步研究表明，与蛇河平原上较古老的火山场有关的泉水中存在异养微生物。提出了系统表征爱达荷州斯内克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变化。了解地下热液系统中自养的、以氢为基础的微生物群落如何随时间变化，以及泉水中有机物的反应性和组成的伴随变化，有助于了解早期地球生命的发展。具体而言，将确定泉水中存在的古细菌和细菌的相对比例，并使用针对适当系统发育或功能基因的特异性引物集，使用定量PCR评估能够进行特定类型异养代谢（即硫酸盐，铁和硝酸盐还原）的细菌的比例。与此同时，将记录泉水中溶解有机物（DOM）的化学和同位素组成，以评估底物生物利用度的变化，并确定这种物质如何反映常驻微生物群的组成。从自养到异养微生物群落的明显转变为研究特定生物过程在DOM成岩作用和保存在环境中的难降解有机物的产生中的作用提供了机会。这些数据将用于描述在大约1000万年的时间框架内深部热液系统的变化和生态进程。

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.