LExEn: Molecular Microbial Ecology and Biogeochemistry of Methane Hydrates and Brine Pools: Distribution and Activity of Microorganisms in Two Extreme Deep Sea Environments

墨西哥湾海底蕴藏着大量的液态和气态碳氢化合物，覆盖在侏罗纪厚厚的盐层上。管道或集中流动区域允许产热碳氢化合物从深层储层快速垂直迁移到沉积物-水界面，并最终进入水柱。盐与烃系统的紧密结合导致了盐水与烃（油气）的频繁共运移。到达地表后，这些流体的共同迁移创造了独特的极端环境，能够支持多产的微生物群落和复杂的基于化学合成的食物网。墨西哥湾的环境因油气的赋存方式而变得复杂。在一种极端情况下，游离气体和/或液态油是海底盐水池或深海中含有的复杂流体的组成部分。这些池中的流体是高盐的，温度可以达到40摄氏度或更高，并可能以喷出物或泥石流的形式夹带大量的淤泥或粘土。在另一个极端，碳氢化合物和硫化氢与水形成冰状的包合物，称为天然气水合物。相对而言，人们对生活在这些环境中的微生物类型、它们的遗传多样性或它们的生态学和生态生理学知之甚少。该项目将测试以下假设：盐水和水合物形成了不同的微生物生态位，其中包含专门的群落和功能，微生物活动与这些系统的地球化学之间的动态相互作用产生了可以在环境中检测到的独特的地球化学信号。通过对微生物和遗传多样性的分析，确定群落的关键功能群和系统发育群。然后，可以通过测量生物地球化学速率（例如硫化物和甲烷氧化、甲烷生成、硫酸盐还原）将这些生物与它们的特征活动联系起来。这些过程的证据记录在微生物群和周围环境中，可以通过细胞和环境分子的稳定同位素分析来揭示。这些信息将有助于深海微生物学领域的研究，并有助于更好地了解微生物对其他行星上可能存在的独特环境（例如木卫二上的水合物）的适应。

The Gulf of Mexico seafloor contains vast reservoirs of liquid and gaseous hydrocarbons that overlay thick accumulations of Jurassic salt. Conduits, or focused flow regions, permit rapid vertical migration of thermogenic hydrocarbons from deep reservoirs to the sediment-water interface and, ultimately, into the water column. The close association of salt and hydrocarbon systems results in frequent co-migration of brine and hydrocarbons (oil and gas). Upon reaching the surface, the co-migration of these fluids creates distinct extreme environments capable of supporting prolific microbial communities and complex chemosynthetically-based food webs. The Gulf of Mexico setting is complicated by the mode of hydrocarbon occurrence. At one extreme, free gas and/or liquid oil is a component of a complex fluid contained in seafloor brine pools or diatremes. The fluid in these pools is hypersaline, can reach temperatures of 40 degrees C or greater, and may entrain quantities of silt or clay as ejecta or debris flows. At the opposite extreme, hydrocarbons and H2S form ice-like clathrates with water, called gas hydrates. Relatively little is known about the types of microorganisms dwelling in these environments, their genetic diversity, or their ecology and ecophysiology. This project will test the hypotheses that brines and hydrates form distinct microbial niches containing specialized communities and functions and that the dynamic interaction between the microbial activity and geochemistry of these systems results in distinctive geochemical signals that can be detected in the environment. Key functional and phylogenetic groups in the community will be identified by analysis of microbial and genetic diversity. The organisms can then be linked to their characteristic activities through measurement of biogeochemical rates (e.g. sulfide and methane oxidation, methanogenesis, sulfate reduction). Evidence of these processes is recorded in both the microbiota and the surrounding environment and can be revealed through stable isotopic analysis of cellular and environmental molecules. This information will contribute to the field of deep-sea microbiology and will lead to a better understanding of the microorganisms' adaptations to unique environments that may be present on other planetary bodies (e.g., hydrates on Europa).