Nitrate dependent anaerobic oxidation of methane drives the carbon cycle in authigenic carbonates along the Atlantic and Pacific Margin

Cold seeps over a large depth range along the US Atlantic and Pacific Margin host hot spots of methanotrophic archaea (ANMEs) that carry out anaerobic oxidation of methane (AOM) and favour the precipitation of methane derived authigenic carbonates (MDAC). AOM plays an important role in the long-term storage and removal of methane from the marine carbon cycle leading to the significance of identifying the microbial communities driving AOM in authigenic carbonates. Here we identify the authigenic carbonate microbiome hosted at cold seeps along the Pacific (Queen Charlotte Fault) and Atlantic (Washington Canyon, Norfolk Canyon, Baltimore Canyon, Chincoteague Seep, Pea Island Seep, Blake Ridge) Margins by carrying out an extensive survey using Illumina 16S rRNA, mcrA gene sequencing and metagenomic analyses of MDACs. AOM is usually carried out by symbiotic consortia of ANMEs and sulfate reducing bacteria (SRB) due to the high availability of sulfate in marine habitats. Three distinct ANME clusters (ANME-1, -2, -3) have been detected in association with their SRB partners affiliated to the Desulfosarcina/Desulfococcusand Desulfobulbusgroups. These results are consistent with the detection of distinct archaeal lipid signatures diagnostic for methane oxidizing archaea (archaeol, sn-2-hydroxyarchaeool, pentamethylicosane and crocetane) and their compound specific isotopes from previous work at Norfolk and Baltimore seeps. However, the low relative abundance of ANMEs and/or lack of SRB as well as elevated fatty acid d ¹³C values at all seep sites suggest the importance of a different AOM driver. Our data revealed that nitrate is the main terminal electron acceptor wherebyAOM appears to be nitrate-dependent in the presence of Candidatus Methanoperedens nitroreducens.