Nyegga Coldseep Sediment Metagenome

Anaerobic methanotrophic archaea (ANME) are major players in methane enriched marine sediments reducing the emission of this green-house gas to the Oceans, yet little is known about their in situ metabolisms and interspecies relations. A combined metagenomic and metaproteomic approach was applied to determine the metabolic pathways expressed in a naturally enriched ANME-1 community in cold-seep sediment at Nyegga. In total, 16.6 Mbp sequence information was assembled into contigs and taxonomic analysis revealed a dominance of Archaeal sequences comprising 74 % of the metagenome where ANME-1 constituted 66 % and ANME-2 0.01 %, respectively. Open reading frame translations were used as database for protein identifications and of the 356 proteins identified in the sediment sample, 245 were associated with ANME-1. All enzymes of the reverse methanogenesis pathway, except N5N10-Methylene-Tetrahydromethanopterin reductase (mer), were expressed in the sediments by ANME-1, hence validating on the protein level, anaerobic methane oxidation via this pathway in cold seep sediments. Any knowledge on bypassing-mechanisms of the mer-catalyzed reaction was neither retrieved from the metagenomic nor the metaproteomic data. However, although constituting, a minor fraction of the microbial community, an ANME-2c affiliated mer was expressed as well as the subunits of the key enzyme methyl-CoM reductase. The key enzymes, APS-reductase and sulfite reductase in the dissimilatory sulfate-reduction pathway were expressed in the sediments by at least two different members of Deltaproteobacteria. The approach is applicable to reveal dominating in situ metabolism on the protein level of ANME-dominated sedimentary ecosystems.