Characterization of microbial structure and function in the sulfate-methane transition zone(SMTZ) of the gas hydrate-bearing sediment in the Ulleung Basin in the East Sea

Abstract

We investigated microbiological parameters (diversity and abundance of dsrAB gene and mcrA gene, and prokaryotic composition based on 16S rRNA gene) to characterize microbial communities associated with biogeochemical parameters (sulfate reduction rate (SRR) and the distribution of CH4, SO4 2-, CO, and H2) in the sulfate-methane transition zone (SMTZ) of the gas hydrate-bearing sediment in the southwestern continental slope of the Ulleung Basin (UB) in the East Sea. From the profiles of SO4 2-and CH4, the SMTZ was clearly defined between 0.6 and 1.4 mbsf. Highest peaks in sulfate reduction rate (12.6 nmol cm-3d-1 at 0.65 mbsf), carbon monoxide (83 μM), gene copies of dsrA (6.2 x 106 copies cm-3 at 0.5 mbsf) and mcrA (11.6 x 106 copies cm-3 at 0.8 mbsf) were appeared within the SMTZ. We suggest that CO in the SMTZ might be one of intermediate metabolic products of AOM independent sulfate reduction, which is rapidly consumed by CO oxidizer coupling to sulfate reducer. Bacterial communities were dominated by members of the uncultured candidate division JS1 (59-66.7%) group and Chloroflexi (9.2-21%) of total bacterial clones. The uncultured candidate division JS1 group might be responsible for breakdown of organic matter in the SMTZ of the UB. Both Deep-Sea Archaeal Group (10-45%, DSAG/MBGB) and Marine Benthic GroupD (40-52%, MBGD) appeared to be dominant archaeal groups associated with the Ae reduction rate (SRR) and the distribution of CH4, SO4 2-, CO, and H2) in the sulfate-methane transition zone (SMTZ) of the gas hydrate-bearing sediment in the southwestern continental slope of the Ulleung Basin (UB) in the East Sea. From the profiles of SO4 2-and CH4, the SMTZ was clearly defined between 0.6 and 1.4 mbsf. Highest peaks in sulfate reduction rate (12.6 nmol cm-3d-1 at 0.65 mbsf), carbon monoxide (83 μM), gene copies of dsrA (6.2 x 106 copies cm-3 at 0.5 mbsf) and mcrA (11.6 x 106 copies cm-3 at 0.8 mbsf) were appeared within the SMTZ. We suggest that CO in the SMTZ might be one of intermediate metabolic products of AOM independent sulfate reduction, which is rapidly consumed by CO oxidizer coupling to sulfate reducer. Bacterial communities were dominated by members of the uncultured candidate division JS1 (59-66.7%) group and Chloroflexi (9.2-21%) of total bacterial clones. The uncultured candidate division JS1 group might be responsible for breakdown of organic matter in the SMTZ of the UB. Both Deep-Sea Archaeal Group (10-45%, DSAG/MBGB) and Marine Benthic GroupD (40-52%, MBGD) appeared to be dominant archaeal groups associated with the A