220 Chapter 7 We additionally investigated the genetic features that could be indicative of a potential interdependency of the Desulfobacterota class QYQD01 and “Ca. Methanoperedens” spp. to sustain syntropy. The recovered Desulfobacterota class QYQDO1 MAG contained the full respiratory sulfate reduction pathway that all “Ca. Methanoperedens” spp. lacked. We found a total of 18 MHC encoded in the “MAG Desulfobacterota class QYDO1” (Figure 5 and Supplementary Table 8). The largest MHC of “MAG Desulfobacterota class QYDO1” was encoded within an operon comprising four adjacent sequences. These sequences encoded two MHC proteins - one with 12 heme binding motifs and another with 26 heme binding motifs - including a peptidyl‐prolyl isomerase (or PPIase) sequence containing 5 heme binding motifs, and a small ORF of unknown function. The second gene cluster encoding large MHCs encoded two cytochromes with 11 and 12 hemebinding motifs, respectively, and an upstream Adenosine monophosphate (AMP) nucleoside-encoding protein plus two other cytochrome C assembly and biogenesis proteins (Supplementary Table 8). Additionally, we also considered the syntrophic lifestyle of SRB associated with marine ANME, and included putative extracellular polysaccharides and protein complexes that could aid in the interaction with “Ca. Methanoperedens” as described in Murali et al. (2023) (Supplementary Table 12). Consistent with our observations on the aggregate formation mechanisms of “Ca. Methanoperedens” (Supplementary Table 9), the presence of certain marker genes in the “MAG Desulfobacterota class QYQD01” supports ANME/SRB interaction and communication (Supplementary Table 12). These structures include type IV pili (EET mechanism), the type VI secretion system (for intercellular communication), and potential adhesins for cellular adhesion, such as the trimeric autotransporter adhesin YadA-like head domain (Supplementary Table 12). We also analyzed some hallmark genomic traits that could suggest a free-living lifestyle of Desulfobacterota class QYQD01 as a putative autotrophic SRB. The “MAG Desulfobacterota c. QYQD01” included the potential for carbon fixation via the Wood–Ljungdahl pathway. We also recovered non-energy conserving cytosolic hydrogenases (NiFe group 3c) for our study’s MAG and the three other Desulfobacterota class QYQD01 MAGs included in the genome tree (Figure 5A).
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