206 Chapter 7 S-AOM ANMEs and their partner SRB bacteria (McGlynn et al., 2015; Meyerdierks et al., 2010), the presence of multiple MHCs in “Ca. Methanoperedens” spp. begs the question of whether they could also live in syntropy with SRBs in sulfate-rich freshwater ecosystems. One of the earliest reports of the potential of “Ca. Methanoperedens” spp. mediating freshwater S-AOM came from sediments of the meromictic Lake Cadagno (Switzerland) (Su et al., 2020), where anoxic incubation experiments with methane, different electron acceptors, combined with molybdate as an inhibitor of bacterial sulfate reduction, revealed that AOM was predominantly sulfate-dependent. Moreover, 16S rRNA gene-based analyses showed a striking co-occurrence along the sediment depth profile of several “Ca. Methanoperedens” Amplicon Sequencing Variants (ASVs) and one single “Desulfobulbaceae” ASV, now reclassified as “uncultured Desulfobacterota” according to SILVA v138.2. This observation suggests that “Ca. Methanoperedens” is probably not responsible for the reduction of sulfate itself but might oxidize methane in syntrophy with an SRB partner. In this study, we aim to elucidate the diversity and the metabolic potential of the “Ca. Methanoperedens” phylotypes in the sediments of Lake Cadagno, as well as of their putative syntrophic SRB partner. For this, we combined data from long-term sediment incubations with different electron acceptors and 13C-methane oxidation, 16S rRNA gene amplicon sequencing and metagenomic analyses. Our findings deepen the understanding of the mechanisms involved in freshwater S-AOM, and support a potential syntrophic interaction with “Ca. Methanoperedens” and a cooccurring Desulfobacterota. MATERIALS AND METHODS Study workflow In Lake Cadagno sediments, rates of anaerobic oxidation of methane (AOM-R), the abundances of “Ca. Methanoperedens” and the uncultured Desulfobacterota ASVs peaked at intermediate depths (19-25 cm), where methane, sulfate, and sulfide were present at concentrations of 2-3 mM, ~ 100 µM, 300-600 µM, respectively (Figure 1A). Figure 1A provides a graphical representation of the relevant data aforementioned
RkJQdWJsaXNoZXIy MTk4NDMw