256 Chapter 8 efficiency in methane and nitrogen removal, controlling hydraulic and solid retention time will be key considering the slow growing nature of these N-DAMO consortia. In Chapter 5, we tested the tolerance and resilience of “Ca. Methanoperedens” to short-term and long-term sulfide exposure. We suggested the putative role of Group III Dsr-LP sulfite reductases as sulfite detoxification mechanism in “Ca. Methanoperedens”. Future work with enzymatic assays including purified or heterologously expressed Group III Dsr-LP sulfite reductases with nitrite and sulfite as substrates will help disentangle the promiscuity and affinity of Group III Dsr-LP sulfite reductase in “Ca. Methanoperedens”. Such investigations will aid to develop Group III Dsr-LP sulfite reductase as functional marker for sulfite/ nitrite detoxification specific for “Ca. Methanoperedens” absent in marine ANME. In Chapter 6, we detailed the physiological long-term acclimation process of the freshwater-adapted “Ca. Methanoperedens Vercelli” to marine salinity conditions in a bioreactor. We identified N(ε)-acetyl-β-L-lysine as a crucial osmolyte produced exclusively by “Ca. Methanoperedens” in the enrichment culture under increased osmotic pressure. This osmolyte is synthesized via the gene pair kamA and ablB, which play a key role in the organism adaptation to saline conditions and might have been horizontally transferred. We also revealed the role of polyhydroxyalkanoates (PHAs) and sialic acids associated with the Extracellular polymeric substances (EPS) layer as coping mechanisms for salt stress. Follow up studies could focus on employing different salts to disentangle the effects of chlorinated vs non-chlorinated salt in the methane oxidation potential of freshwater “Ca. Methanoperedens”. To better understand sialic acid production in the “Ca. Methanoperedens” culture, future studies could use lectin staining combined with fluorescent or enzyme-conjugated secondary reagents alongside FISH. This approach would be similar to the method described in this chapter, which links “Ca. Methanoperedens” -targeted FISH with PHAs. In Chapter 7, we explored the flexibility of “Ca. Methanoperedens” to interact with SRB in the sediment of meromictic Lake Cadagno. Combining in situ sediment analysis and long-term incubations with sulfate and manganese oxides, we
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