Signatures of anaerobic methanotrophic communities in gas hydrate-bearing sediments of the Chukchi Sea

Abstract

Anaerobic oxidation of methane with sulfate-reduction by anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB) is an important process in the methane cycle of marine environments, which is regarded as a major sink of the potential greenhouse gas. However, little is known about metabolic relationship between ANMEs and their sulfate-reducing partners due to the lack of culture representatives. We investigated the microbial communities of gas hydrate-bearing sediments of the Chukchi basin along the depth in combination with geochemical analysis. ANME-1 and sulfate-reducing Deltaproteobacteria were predominant accounting for 97.3% of archaeal communities and 44.3% of bacterial communities, respectively at sulfate-methane transition zone (~120 cm below seafloor). To link metabolic functions with specific microbial populations, genome-centric metagenomic analysis was performed. The assembled metagenomic sequence data generated 1.52 Mb and 2.22 Mb genomes of ANME-1 and sulfate-reducing Deltaproteobacteria. The completeness of ANME-1 and sulfate-reducing Deltaproteobacteria analyzed by single copy marker gene were 80.1% and 86.2%, respectively. ANME-1 genome contains genes for key metabolic enzymes of reverse methanogenesis pathway (except N5,N10-methylene tetrahydromethanopterin reductase) and sulfate-reducing Deltaproteobacteria possesses a complete set of genes for dissimilatory sulfate reduction pathway. We will further investigate the syntrophy and microbial consortia formation to confirm the metabolic coupling between ANME1 and SRB in controlling methane removal.