Microbial Community Structure Associated with Biogeochemical Processes in the Sulfate–Methane Transition Zone (SMTZ) of Gas-hydrate-bearing Sediment of the Ulleung Basin, East Sea

We investigated the biogeochemical constituents, microbial communities and functional genes (mcr and dsr) associated with anaerobic methane oxidation and sulfate reduction, and metabolic activities by sulfate reduction in the sulfate-methane transition zone (SMTZ) of gas-hydrate-bearing sediment of the Ulleung Basin in the East Sea. Maxima in the sulfate reduction rate (12.6nmolcm(-3) d(-1)), CO concentration (83M), and gene abundances of dsrA (9.1 x 10(6) copiescm(-3)) and mcrA (11.6 x 10(6) copiescm(-3)) occurred in the SMTZ. The peaks of CO consistently found in the SMTZ suggested that CO is an intermediate metabolic product related to methane oxidation. Candidate division JS1, the predominant bacterial group that comprised 59.0-63.7% of the 16S rRNA gene sequences, was recognized as an important organic carbon oxidizer. Both Marine Benthic Group D (MBGD) and Marine Benthic Group B (MBGB), which constituted 40.8-52.9 and 10.3-43.9% of the 16S rRNA gene sequences, respectively, were the dominant archaeal groups. Analysis of functional gene diversity revealed that anaerobic methanotroph-1-related phylotypes appeared to be the major CH4 oxidizer, whereas Firmicutes-like group was a predominant sulfate reducer in the 0.8mbsf in SMTZ with low SO42- concentration. Overall results indicated that JS1 and two archaeal groups (MBGB and MBGD) seem to play a significant role in carbon and elements cycles in the gas-hydrate-bearing subsurface sediment of the Ulleung Basin.This research was supported by EAST-1 (East Asian Seas Time Series) Program; K-LTMER (Korean-Long-term Marine Ecological Research) Program; Development of Manned Submersible, Unmanned Underwater Vehicle; and Supporting Infrastructure by the Korean Ministry of Oceans and Fisheries