Distribution and Diversity of Bacteria and Archaea in Marine Sediments Affected by Gas Hydrates at Mississippi Canyon in the Gulf of Mexico

The microbial community structures of gas hydrate-bearing (Core 9) and non-hydrate-bearing (Core 1) marine sediments were investigated at Mississippi Canyon (MC) 118 in the Gulf of Mexico. Quantification by quantitative competitive (QC)-PCR showed that bacterial abundance was 2-3 orders of magnitude higher than archaeal abundance in these cores. Sulfate-reducing bacteria (SRB) were present at 103-104 dsrAB gene copies/g in both cores; methanogens or anaerobic methanotrophs were only present in Core 9 (102-105 mcrA gene copies/g). Denaturing gradient gel electrophoresis (DGGE) showed distinct patterns of bacterial community structure between Core 9 and Core 1 with epsilon-Proteobacteria predominating in the former and -Proteobacteria in the latter. Clone libraries were successfully constructed for both Archaea and Bacteria using functional genes (mcrA and dsrAB, respectively). The mcrA gene was present in Core 9, suggesting enhanced abundance or activity of methanogens or methane-oxidizing archaea in the hydrate-impacted sediment. The mcrA gene sequences were dominated by group c-d and group e. The majority (80%) of the dsrAB gene sequences fell into Syntrophobacteraceae-related group. This study indicates that microbial community structures are considerably different between the hydrate-bearing and non-hydrate-bearing sediment at MC 118. Our study is among the initial steps toward a comprehensive and long-term monitoring of microbial dynamics associated with gas hydrates in the Gulf of Mexico.