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

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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).