THE MICROBIAL ECOLOGY OF GAS HYDRATES

Gas hydrates are the subject of intense investigation owing to their potential use as an alternative energy resource, possible effects on sea-floor stability, change in climatic conditions, and presence on other planets and satellites. Numerous groups are also investigating the biological communities found in connection with hydrate deposits at marine seep sites. While the macrofauna (e.g., vestimentiferan tubeworms, methanotrophic mussels, bivalves and methane-hydrate-dwelling worms) of these chemosynthetic communities have been the subject of study for more than a decade, surprisingly much less is known about the free-living microorganisms associated with either the dense Beggiatoa sp. mats present at many of these locales or in the sediments containing hydrates or within hydrates themselves. A number of geochemical-based studies have demonstrated significant contributions of sulfate reduction and anaerobic methane oxidation (AMO) activities to the cycling of carbon in methane seep sediments with naturally occurring hydrates. In addition, the phylogenetic diversity of extant microbial communities has also characterized. Although it has been proposed that AMO is mediated by a syntrophic coupling between archaeal (i.e., ANME-1 or ANME-2 groups) and sulfate reducing bacterial (i.e., Desulfosarcina sp.) partners, recent evidence by some investigators suggests that such a specific association may not always be necessary for AMO. In this talk, the microbial ecology of free-living prokaryotes extant in the hydrocarbon-rich Gulf of Mexico seep sediments and associated gas hydrate habitats will be discussed. In addition, data will also be presented highlighting the metabolically active microbial constituents within sediment-free gas hydrate and Beggiatoa-mat dominated hydrate-containing seep sediments.