Methanotrophic community structure and metabolic potential in the sulfate–methane transition zone of the ARAON mounds, Arctic Chukchi Sea

Anaerobic oxidation of methane (AOM) mediated by archaea is a pivotal process for methane consumption in gas seepage-associated sediments. Despite its importance in regulating methane flux, the ecological roles and metabolic potential of microbial communities involved in AOM remain poorly understood in Arctic regions. In this study, we investigated the microbial community structures and methanotrophic signatures in sediments from gas hydrate-bearing and non-gas hydrate-bearing sites in ARAON Mounds (AMs) and reference sites. Microbial communities in AMs were distinct from those in reference sites, with high relative abundances of Euryarchaeota (45.5 ± 11%), Lokiarcheota (35 ± 6.1%), and Atribacterota (50.1 ± 23.3%). Anaerobic methanotrophic archaea (ANME) showed site- and depth-specific distributions, with ANME-1a, ANME-1b, and ANME-2c predominating the sulfate-methane transition zone (SMTZ) of the gas hydrate-bearing sites, and ANME-1a prevailing at non-gas hydrate-bearing sites. Sulfate-reducing bacteria (SRB) affiliated with Seep-SRB1 co-occurred with ANME-1a and ANME-1b within the AMs. Metagenome-assembled genomes (MAGs) of ANME-1b and ANME-2c recovered from the SMTZ of the gas hydrate-bearing site (AM6) harbored key AOM-related genes, and their putative syntrophic bacterial partner, ETH-SRB1, possessed essential genes for sulfate reduction. Additionally, Lokiarchaeota and Atribacterota MAGs encoded genes involved in protein degradation, fermentation, and hydrogen metabolism, indicating their possible roles in methane cycling. Collectively, these results reveal distinct microbial assemblages and their functional genomic traits, suggesting niche specialization associated with methane oxidation potential at the SMTZ of the gas hydrate-bearing site.