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

Abstract

<p>We investigated the biogeochemical constituents, microbial communities and functional genes (<i>mcr</i> and <i>dsr</i>) 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 (12.6 nmol cm⁻³ d⁻¹), CO concentration (83 μM), and gene abundances of <i>dsrA</i> (9.1 × 10⁶ copies cm⁻³) and <i>mcrA</i> (11.6 × 10⁶ copies cm⁻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 <i>Firmicutes</i>-like group was a predominant sulfate reducer in the 0.8 mbsf 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.</p