It has been proposed that Candidatus Methylomirabilis oxyfera of the NC10 group can oxidize methane anaerobically without an archaeal partner [30, 31]. A pathway of “”intra-aerobic”" methane oxidation where an intracellular supply of oxygen is produced by metabolism of nitrite to oxygen and dinitrogen has been suggested. This intracellularly produced oxygen is then used for the oxidation of methane via pmoA . Reads assigned to NC10 were significantly overrepresented (99% confidence interval) in the 10-15 cm metagenome compared to the 0-4 cm metagenome. Still, there was far less reads (approximately 1:100) assigned to NC10 than to ANME-1 in the 10-15 PCI-32765 in vivo cm metagenome.
Methane oxidation pathways To gain insight into the metabolic pathways for methane oxidation at the Tonya Seep, we annotated
the reads from each metagenome to KO and EC numbers and plotted them onto KEGG pathway maps. In this way, the methane monooxygenase gene (EC: 18.104.22.168) was identified in the 0-4 cm sample, supporting the idea of aerobic methane oxidation in this sediment horizon. This gene was not detected in the 10-15 cm metagenome. All the genes needed for AOM/methanogenesis, including mcrA (EC: 22.214.171.124), were detected in Selleck CH5183284 the 10-15 cm metagenome (Figure 5). In the 0-4 cm metagenome, the genes for methylenetetrahydromethanopterin dehydrogenase (mtd, EC: 126.96.36.199) and methenyltetrahydromethanopterin cyclohydrolase (mch, EC: 188.8.131.52) were not detected. This is likely due to the low abundance of reads assigned to Euryarchaeota
and “”Archaeal environmental samples”", and thereby low coverage of genes encoded by these taxa, in the 0-4 cm metagenome. In total, 1757 reads were assigned to these taxa in the 0-4 cm metagenome. With an average sequence length of 413 bases this gives a total of 0.7 M bases, while the average ANME-1 genome size is estimated to be 3.3-3.6 Mbp (Table 1) . Figure 5 Anaerobic oxidation of methane/methanogenesis pathway. The figure is based on the KEGG-map for methane metabolism and includes the enzymes involved in methanogenesis and reverse methanogenesis. Colours are used to indicate from which 5-Fluoracil cell line metagenome the enzymes were identified by KAAS annotation. Anaerobic oxidation of methane is usually associated with dissimilatory sulphate reduction, where adenylyl-sulphate reductase (EC: 184.108.40.206) first reduces sulphate to sulphite before dissimilatory sulphite reductase (EC: 220.127.116.11) reduces sulphite to sulphide . These genes were detected in both metagenomes. check details marker genes To obtain a more precise picture of taxa actually capable of methane oxidation in our sediment, the metagenomes were compared with libraries of marker genes for methane oxidation. Estimated probabilities for identifying the specific marker genes were used to calculate expected hits to marker genes in a scenario where all organisms in the communities contained the gene in question (Additional file 1, Table S1).