Zonation of the active methane-cycling community in deep subsurface sediments of the Peru trench

• Main Authors: Lever, Mark A., Alperin, Marc J., Hinrichs, Kai-Uwe, Teske, Andreas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media 2023
• Subjects: anaerobic oxidation of methane; methanogenesis; carbon isotopes; deep biosphere; mcrA; methane hydrate; subseafloor sediment; ocean drilling; Methane hydrate
• Online Access: https://doi.org/10.17615/dq34-4638; https://cdr.lib.unc.edu/downloads/2v23w516t?file=thumbnail; https://cdr.lib.unc.edu/downloads/2v23w516t

The production and anaerobic oxidation of methane (AOM) by microorganisms is widespread in organic-rich deep subseafloor sediments. Yet, the organisms that carry out these processes remain largely unknown. Here we identify members of the methane-cycling microbial community in deep subsurface, hydrate-containing sediments of the Peru Trench by targeting functional genes of the alpha subunit of methyl coenzyme M reductase (mcrA). The mcrA profile reveals a distinct community zonation that partially matches the zonation of methane oxidizing and –producing activity inferred from sulfate and methane concentrations and carbon-isotopic compositions of methane and dissolved inorganic carbon (DIC). McrA appears absent from sulfate-rich sediments that are devoid of methane, but mcrA sequences belonging to putatively methane-oxidizing ANME-1a-b occur from the zone of methane oxidation to several meters into the methanogenesis zone. A sister group of ANME-1a-b, referred to as ANME-1d, and members of putatively aceticlastic Methanothrix (formerly Methanosaeta) occur throughout the remaining methanogenesis zone. Analyses of 16S rRNA and mcrA-mRNA indicate that the methane-cycling community is alive throughout (rRNA to 230 mbsf) and active in at least parts of the sediment column (mRNA at 44 mbsf). Carbon-isotopic depletions of methane relative to DIC (−80 to −86‰) suggest mostly methane production by CO2 reduction and thus seem at odds with the widespread detection of ANME-1 and Methanothrix. We explain this apparent contradiction based on recent insights into the metabolisms of both ANME-1 and Methanothricaceae, which indicate the potential for methanogenetic growth by CO2 reduction in both groups.