Page 67 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

heterotrophic fermenting and syntrophic lifestyles (Nobu et al. 2016b). A recent study by Glass et al. (2019) found candidate JS1 bacteria with low temperature and salinity adaptation in subseafloor gas hydrates. This indicates a wide tolerance range and a preference of JS1 for methane-rich environments. Network analyses support the co-occurrence of candidate phylum JS1 with H2 and formate-scavenging methanogens and propionate metabolizers (Gies et al. 2014). They are less abundant in the deposit layer communities but might play a role in the nutrient cycling of deeper sediments.
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Coriobacteriales, Syntrophobacterales, and the actinobacterial order OPB41 are key members of the deposit layer microbial communities
De novo assembly and consensus binning resulted in a total of 16 MAGs with an estimated genome completeness >50% (data not shown). A total of 81% of the reads were aligned to MAGs. We obtained four nearly complete MAGs (>95% completeness) that were all highly enriched in DL but showed low abundance in AS (average aligned read coverage of the MAGs, <1.5%) and BS (average aligned read coverage of the MAGs, <0.02%) (Table 1). Initial taxonomic classification by CheckM indicated two Coriobacteriales MAGs, one Syntrophobacterales MAG, and one Methanobacteriales MAG that together contained 47% of the mapped reads of the deposit layer microbial community. These four MAGs were analyzed for their potential role in nutrient cycling and natural CPL formation.
The two highly complete Coriobacteriales MAGs contained 20.5% of all mapped DL reads. Although Coriobacteriales were not detected with the 16S rRNA gene survey, the large number of reads aligning to the MAGs indicates their potentially important role in DL. Coriobacteriales are an order within the Actinobacteria that are known for their important role in nutrient cycling of soils (Dignac et al. 2005; Jacquiod et al. 2014). Actinobacteria have a central role in decomposition of dead organic matter, including lignin solubilization (Dignac et al. 2005). A study by Gupta et al. (2018) on acidic mine drainage soils indicated that Coriobacteriaceae can perform extracellular electron transport probably through use of c-type cytochromes and monomethylmenaquinone-6, its major respiratory quinone, as shown by growth on anodes in fuel cells (Clavel, Lepage and Charrier 2014; Zhang et al. 2018). The production of menaquinone-6 homologues of vitamin K2 seems to be a common attribute of the
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