Characterization of archaeal and bacterial communities thriving in methane-seeping on-land mud volcanoes, Niigata, Japan

Abstract

Submarine mud volcanoes (MVs) have attracted signi cant interest in the scienti c community for obtaining clues on the subsurface biosphere. On-land MVs, which are much less focused in this context, are equally important and they may provide insights also for astrobiology of extraterrestrial mud volcanism. Hereby, we characterized microbial communities of the two active methane-seeping on-land MVs, Murono and Kamou, in central Japan. Metataxonomic 16S rRNA sequencing analysis of those sites recovered the dominant archaeal taxa a liated with methanogens. Anaerobic methanotrophs (ANME), with the subgroups ANME-1b and ANME-3, were also recovered from the Murono site albeit a greatly reduced abundance compared to typical submarine MVs. ANME-3 was in fact identi ed for the rst time for land-based MVs. The bacterial sequences a liated to Atribacteria, sulfate-reducing bacteria (SRB), and Fe(III)-reducing bacteria were recovered. SRB and ANME form a syntrophic consortium, which is often found at the sulfate-methane transition zone of submarine MVs where diffused sulfate (SO 4 2-) is constantly enriched from the ocean. Previous investigations speculate that the erupted materials from Murono are originated from the Miocene marine strata, and we hypothesize that the old sea-related juvenile water is the source of additional sulfur-related components for the SRB-ANME consortium at Murono.