217 Methanotrophic flexibility of “Ca. Methanoperedens” and SRB in meromictic Lake Cadagno Methanoperedens 5” showed almost twice the amount of MHC proteins compared to “Sed MAG Methanoperedens 1, 2 and 3”. “MnO2 MAG Methanoperedens” and “Sed MAG Methanoperedens 5” had 44 and 47 MHCs, respectively (Figure 4). Only “Sed MAG Methanoperedens 2 and 5” encoded two and one OmcZ-like subunits possibly forming nanowire proteins, respectively. The other “MnO2 MAG Methanoperedens” did not contain omcZ like genes. Instead, “MnO2 MAG Methanoperedens” (contig_13_120) contained an Extracellular Cytochrome Nanowire (ECN) (Baquero et al., 2023) that shared 98% BLASTp identity with “Ca. Methanoperedens BLZ2” ECN [WP_097300794.1], matching the high AAI (92%) of both MAGs (Supplementary Figure 2). In Ouboter et al. (2024) and Leu et al. (2020a), several gene clusters are described to be involved in EET by “Ca. Methanoperedens”. Therefore, we assessed which MHC genes of the Lake Cadagno “Ca. Methanoperedens” MAGs resembled those clusters. We find that more than half of the MHC proteins in “MnO2 MAG Methanoperedens” and in “Sed MAG Methanoperedens 3 and 5” showed high homology with MHC proteins expressed in the reference “Ca. Methanoperedens” spp. (Figure 4). For example, in “MnO2 MAG Methanoperedens”, 7 out of the 44 MHC proteins were related to those highly expressed in “Ca. Methanoperedens” spp. grown with manganese oxides as the electron acceptor, while 4 were related to MHC proteins with low expression under iron-oxide-reducing conditions. In “Sed MAG Methanoperedens 5”, 9 out of the 49 MHC proteins corresponded to MHC proteins expressed in the iron-AOM “Ca. Methanoperedens” enrichment, with the majority showing low expression levels, and a few matching those with medium or high expression (Figure 4). Furthermore, “Sed MAG Methanoperedens 5” omcZ-like genes appeared to be clustering close to the highly expressed omcZlike gene in “Ca. Methanoperedens ferrireducens” performing Fe-AOM (Figure 4 and Supplementary Figure 3). We also examined the presence of additional EET electroconductive structures. We identified type IV pilus assembly proteins in all Lake Cadagno “Ca. Methanoperedens” MAGs. Furthermore, we investigated the formation mechanisms of extracellular polymeric substances (EPS), as these could facilitate the development of ANME/SRB consortia through the formation of cell aggregates 7
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