BACTERIAL METHANE OXIDATION IN SEA-FLOOR GAS HYDRATE - SIGNIFICANCE TO LIFE IN EXTREME ENVIRONMENTS

Samples of thermogenic hydrocarbon gases, from vents and gas hydrate m ounds within a sea-floor chemosynthetic community on the Gulf of Mexic o continental slope at about 540 m depth, were collected by research s ubmersible. Our study area is characterized by low water temperature ( mean = 7 degrees C), high pressure (about 5400 kPa), and abundant stru cture II gas hydrate, Bacterial oxidation of hydrate-bound methane (CH 4) is indicated by three isotopic properties of gas hydrate samples. R elative to the vent gas from which the gas hydrate formed, (1) methane -bound methane is enriched in C-13 by as much as 3.8 parts per thousan d PDB (Peedee belemnite),(2) hydrate-bound methane is enriched in deut erium (D) by as much as 37 parts per thousand SMOW (standard mean ocea n water), and (3) hydrate-bound carbon dioxide (CO2) is depleted in C- 13 by as much as 22.4 parts per thousand PDB, Hydrate-associated authi genic carbonate rock is also depleted in C-13. Bacterial oxidation of methane is a driving force in chemosynthetic communities, and in the c oncomitant precipitation of authigenic carbonate reek that modifies se a-floor geology, Bacterial oxidation of hydrate-bound methane expands the potential boundaries of life in extreme environments.