Page 68 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 3. Metal corrosion protection potential of methanogenic communities
Coriobacteriaceae (Clavel, Lepage and Charrier 2014). The potential for extracellular electron transport can be an important feature when iron is abundantly present.
16S/23S rRNA genes were only obtained from one of the two Coriobacteriaceae MAGs. The 16S rRNA gene (1,509 nucleotides [nt]) was most identical (97% nt identity) to an uncultured Actinobacterium clone EMTBiocatB-13, from the biocathode of a thermophilic fuel cell catalyzing electromethanogenesis (KM819482.1) (Fu et al. 2015). Regarding cultivated bacteria, it had the highest identity to Raoultibacter sp. strain Marseille-P8396 (90% nt identity). The 23S rRNA gene (2,633 nt) was most identical (85% nt identity) to Gordonibacter massiliensis Marseille-P2775 isolated from a human fecal sample (Traore et al. 2016). These findings indicate that the two environmental Coriobacteriales MAGs are distantly related to Coriobacteriales isolated from human microbiomes. 30S and 50S rRNA analyses showed highest identity of the first Coriobacteriales MAG (89% average amino acid [aa] identity) to Actinobacteria bacterium 66_15 isolated from a terrestrial environment in the Schrader Bluff formation on the Alaska North Slope (taxonomy ID 1635289) (van der Kolk, Flaig and Hasiotis 2015). The second Coriobacteriales MAG was most identical (90% aa identity) to Actinobacteria bacterium HGW-Actinobacteria-1 and Actinobacteria-6, which were detected in deep terrestrial subsurface sediments that were actively transforming H2 and metals (Hernsdorf et al. 2017) (see Tables S10, S11, S14, S15 in the supplemental material).
Both MAGs contained the Wood-Ljungdahl pathway for carbon fixation (Tables S11 and S15). From the second MAG, two ACS genes were identified with highest identities to the Actinobacteria bacterium HGW-Actinobacteria-6 (94% and 88% aa identities) (Hernsdorf et al. 2017) (Table S15). The most closely related ACS sequences of cultivated representatives belonged to Thermodesulfovibrio thiophilus and T. aggregans (67% and 65% aa identities, respectively).
The functional roles of environmental Coriobacteriales species are mostly unknown (Daquiado et al. 2016). Desulfobacterales and Coriobacteriales were detected as main benzene degraders in a DNA-stable isotope study with [13C]-benzene (Noguchi et al. 2014). Comparative analyses of 12C and 13C-labeled samples further indicated the enrichment of Methanosarcinales (Noguchi et al. 2014). Here, we observed two Coriobacteriales MAGs in cooccurrence with methanogens, supporting a central role in organic matter-degrading methanogenic cultures.
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