14 Summary short-term and particularly after long-term (6.5 weeks) exposure. During the shortterm sulfide exposure, sulfide detoxification seemed to proceed via sulfide-oxidizing bacteria. Long-term exposure at 0.25 mM sulfide/day stimulated the expression of Group III Dsr-LP sulfite reductases belonging to “Ca. Methanoperedens” spp. Furthermore, “Ca. Methanoperedens” storage polymers were used during the longterm sulfide exposure probably linked to the stress response. In Chapter 6, we reported the long-term bioreactor acclimation of freshwateradapted “Ca. Methanoperedens Vercelli” to marine salinities. We described N(ε)-acetyl-β-L-lysine as a key osmolyte that is exclusively produced by “Ca. Methanoperedens” in the enrichment via the gene pair kamA and ablB. We expanded the production potential of N(ε)-acetyl-β-L-lysine across a universal evolutionary tree focused on archaea and demonstrated that horizontal gene transfer (HGT) from Firmicutes gave rise to the production potential of this osmolyte in ANME archaea. We additionally hypothesize that N(ε)-acetyl-β-L-lysine production potential might have been acquired from “Ca. Methanoperedens spp.” into Borgs also via HGT. Both polyhydroxyalkanoates and sialic acids or negatively charged monosaccharides belonging to the extracellular polysaccharide layer, were linked to “Ca. Methanoperedens” and indicated to be employed as coping mechanisms for salinity stress. In Chapter 7, we expanded on the electron acceptor flexibility of “Ca. Methanoperedens” and addressed the possibility for S-AOM in the sediment of meromictic Lake Cadagno. We described the interaction of “Ca. Methanoperedens” spp. with an undescribed Desulfobacterota class QYQD01. In this chapter, we additionally recovered five different “Ca. Methanoperedens” MAGs from sediment and incubations with sulfate and manganese oxide. We described the potential of these MAGs to engage in Extracellular Electron Transfer (EET) via distinct Multi-heme-Cytochrome (MHCs) or OmcZ nanowires. Furthermore, we explored the genomic traits of Desulfobacterota class QYQD01 as a facultative sulfate reducing bacteria (SRB) syntroph. We also investigated the widespread co-abundance of Desulfobacterota class QYQD01 with “Ca. Methanoperedens” species mainly in marine and groundwater systems.
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