Abundant taxa are defined as taxa comprising ≥ 0.1 % of all assigned reads in one or more metagenomes. Most taxa differing significantly in abundance from the Oslofjord metagenomes were detected in Tplain and Tpm1-2 (Table 3). Genera of the phylum Proteobacteria (especially the PI3K inhibitor classes Alphaproteobacteria and Gammaproteobacteria), as well as genera of the archaeal phylum Thaumarchaeota, were most frequently overrepresented in these metagenomes, while genera sorting under the bacterial phylum Firmicutes and the archaeal phyla Euryarchaeota

and Crenarchaeota Selleck Roscovitine were most frequently underrepresented compared to the Oslofjord metagenomes (Additional file 10: Table S5). These trends were also supported by the PCA plot (Figure

3A). Abundant taxa at the genus level We were primarily interested in studying differences among the abundant taxa at the genus level (abundant taxa defined in this study as taxa with more than 0.1% of the reads assigned in one or more metagenomes), since these taxa are likely to have a higher influence on the biochemical activities at the different sites. Altogether 48 abundant bacterial and archaeal taxa were identified at the genus level in the seven metagenomes (Additional file 11: Table S6). Significant differences between one or more Troll metagenomes compared to both Oslofjord metagenomes GS-9973 in vivo were detected among 21 of these in the STAMP analysis (Figure 4). Of these 13 were detected in Tplain and 17 in Tpm1-2, respectively (Table 3). Nine genera were detected in both Tplain and Tpm1-2 (Figure 4). Figure 4 Significant differences in prokaryote taxonomy between Troll and Oslofjord metagenomes. The figure shows abundant taxa at the genus level (≥ 0.1 % of the reads in one or more metagenomes) that were classified as significantly different in C59 at least one Troll metagenome compared to both Oslofjord metagenomes

in the STAMP analysis. Troll metagenomes significantly different from the Oslofjord metagenomes are marked by red arrows. Interestingly, both autotrophic nitrifying genera (Nitrosopumilus, Nitrospira and Nitrosococcus) and oligotrophic marine gammaproteobacteria (OMG: BD1-7, marine gamma proteobacterium HTCC2148 and “unclassified Gammaproteobacteria (miscellaneous)”) were overrepresented in all Troll metagenomes, although not significantly in all, compared to the Oslofjord metagenomes (Figure 4). Methanotrophic genera To see if the sediments from the Troll pockmarks had an increased potential for methane oxidation we searched the metagenomes for known methanotrophic taxa. ANME is not recognized as an independent taxon in the NCBI taxonomy, but an inspection of the reads assigned to “environmental samples, Archaea” showed that these were further assigned to ANME fosmids isolated from Eel River [10] or to “uncultured archaeon”.