45% and 13.03% of the reads respectively. In contrast, “”Archaeal environmental samples”" represented only 0.15% of the 0-4 cm metagenome, where reads assigned to Proteobacteria representing 31.07% were clearly most abundant (Table 1). Euryarchaeota was also significantly better represented Ro-3306 in the 10-15 cm metagenome. Table 1 Reads assigned to bacterial and archaeal taxa at the phylum-level

in MEGAN Domain Phyla 0-4 cm metagenome 10-15 cm metagenome Significant     Reads assigned Percent of reads Reads assigned Percent of reads difference 1 Bacteria Proteobacteria 82318 31.07 30020 15.45 *** Bacteria    - Gammaproteobacteria 2 27876 10.52 6442 3.31 *** Bacteria    - Deltaproteobacteria 2 13777 5.20 12015 6.18 *** Bacteria    - Alphaproteobacteria 2 8355 3.15 2416 1.24 *** Bacteria    - Epsilonproteobacteria 2 5198 1.96 877 0.45 *** Bacteria    - Betaproteobacteria 2 3045 1.15 1067 0.55 *** Bacteria    - Zetaproteobacteria 2 282 0.11 77 0.04 *** Bacteria Bacteroidetes 16782 6.34 6073 3.12 *** Tucidinostat in vitro Bacteria Planctomycetes 3657 1.38 2447 1.26   Bacteria Firmicutes 3620 1.37 4445 2.29 *** Archaea Euryarchaeota 1353 0.51 6772 3.48 *** Archaea Archaeal environmental samples 404 0.15 25317 13.03 *** The table presents number of reads assigned

at the phylum level in MEGAN. For the phylum Proteobacteria, subsets of reads assigned proteobacterial classes are shown. All percentages are given as the percentage of total reads for each filtered metagenome. (Only phyla with at least 1% of the total unique reads in one or both samples are included.) 1 *** indicates 99% confidence interval 2 Reads assigned to Proteobacteria at the class level in MEGAN Among the Proteobacteria, Sulfurovum was the most abundant genus in the 0-4 cm metagenome (Additional file 2, Table S2). This sulphur oxidizing genus, with its versatile energy metabolism, is known to thrive in sediments related to hydrothermal Tangeritin seepage where reductive and oxidative states in the mixing zone often fluctuate [26]. Sulfurovum was almost four times more abundant in the 0-4 cm metagenome compared to the 10-15 cm metagenome. This is consistent with oxidative

zones being its preferred habitat [26]. Taxa potentially involved in methane oxidation The methane oxidation measurements in the sediment cores indicated methanotrophic activity at both sediment depths. The metagenomes were searched for reads assigned to known methanotrophic genera that might be involved in methane oxidation. Methylococcus was the predominant aerobic methanotrophic genus in both metagenomes, but was significantly more abundant in the 0-4 cm metagenome where it accounted for 0.16% of the reads compared to the 10-14 cm metagenome where it accounted for 0.04% of the reads (Figure 4 and Additional file 2, Table S2). Although reads assigned to the aerobe MK-8931 order methanotrophs Methylomonas, Methylocella and Methylacidiphilum were also detected, Methylococcus was approximately 10 and 2.