213 Methanotrophic flexibility of “Ca. Methanoperedens” and SRB in meromictic Lake Cadagno and 1.09%. All incubations selected for SRB closer to the Syntrophaceae rather than for the uncultured Desulfobacterota representative, previously described as Desulfobulbaceae (Supplementary Figure 1E). Co-occurrence of “Sed MAG Methanoperedens 1” and SRB Desulfobacterota class QYQD01 supports possible syntrophic interactions To resolve the co-occurrence and potential interaction of ANMEs and SRB in Lake Cadagno, a metagenome analysis was conducted, and five “Ca. Methanoperedens” MAGs were retrieved (Figure 2). Four of the “Ca. Methanoperedens” MAGs were abundant in the original sediment while one MAG (labelled “MnO2 MAG Methanoperedens”, light blue) dominated the MnO2 incubation (Figure 2). The most abundant Methanoperedens MAG in the original sediment sample, “Sed MAG Methanoperedens 1”, contained a full-length 16S rRNA gene that showed 100% identity to one of the sequence variants recovered by Su et al. (2020) (Figure 1, ZOTU202 and Supplementary Figure 4 in original paper). “Sed MAG Methanoperedens 1” sustained its dominance as the main anaerobic methane oxidizer for the unamended control and the sulfate incubation (Figure 2). The numbering of the “Ca. Methanoperedens” MAGs is based on the metagenomic abundance of archaeal MAGs, from most to least abundant, in the co-assembled sediment metagenome (23 cm depth) (Supplementary Table 2). This resulted in “Sed MAG Methanoperedens 1, 2, 3 and 5” (Figure 2), with “Sed MAG 4 c_ Thermoplasmata” being assigned number four. The most prominent SRB MAG in the sediment belonged to the Desulfobacterota class QYQD01, with 5.6 to 6.7% of the reads in sediment 23 cm and 25 cm, respectively (Figure 2 and Supplementary Table 3). “MAG Desulfobacterota c. QYQD01” showed 100% of 16S rRNA gene identity match with the most abundant uncultured Desulfobacterota ZOTU307, previously described as “uncultured Desulfobulbaceae” (Su et al., 2020). The closest related microorganism to “MAG Desulfobacterota c. QYQD01” in the NCBI database is the cultured Desulfobacca acetoxidans DSM11099, with an amino acid identity of 89.7% and 89% query cover. Consistent with the 16S rRNA gene analysis, the abundance of “MAG Desulfobacterota c. QYQD01” decreased to 0.2%, 0.05%, and 0.03% in the unamended control, sulfate, and manganese oxide 7
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