140 Chapter 5 2015). ANME-1, ANME-2abc and ANME-3 are typically found in marine and coastal sediments, where they form consortia with sulfate-reducing bacteria (SRB) to facilitate sulfate-dependent-AOM (S-AOM) (Chadwick et al., 2022; Guerrero-Cruz et al., 2021; Timmers et al., 2017). ANME-2d, or “Ca. Methanoperedens”, contributes to AOM in freshwater anoxic sediments (Chen et al., 2020). These same freshwater anoxic sediments have been used to enrich “Ca. Methanoperedens” in bioreactors (Raghoebarsing et al., 2006; Haroon et al., 2013). Notably, “Ca. Methanoperedens” exhibits a highly versatile metabolism, with the potential for nitrate, iron, and manganese reduction in AOM bioreactors that utilize freshwater anoxic sediments as seed inoculum (Arshad et al., 2017; Cai et al., 2018; Haroon et al., 2013; Leu et al., 2020a; Raghoebarsing et al., 2006; Vaksmaa et al., 2017). In addition, there are growing data correlating sulfate reducers with “Ca. Methanoperedens” for S-AOM in meromictic lakes and in iron-rich groundwater systems (Bell et al., 2022; Su et al., 2020). Estuaries are examples of natural hotspots for methane emissions (Venetz et al., 2023; Żygadłowska et al., 2023; Żygadłowska et al., 2024b) and are dynamic environments for carbon, nitrogen, and sulfur cycling. There areas are sensitive to human-induced changes (Wallenius et al., 2021). Eutrophication in coastal ecosystems leads to a surplus of organic carbon degradation coupled with sulfate reduction resulting in sulfide accumulation. Elevated sulfide levels can disrupt microbial community functions and reduce methane oxidation rates (Dalcin Martins et al., 2024, Chapter 2; Dalcin Martins et al., 2022, Chapter 4). Increasing sulfide concentrations may also inhibit key metabolic processes by damaging copper- and iron-containing cofactors (Jin et al., 1998) and inhibiting methanogenesis (Karhadkar et al., 1987). However, detailed studies on the effect of sulfide on freshwater methanotrophs are lacking. The impact of sulfide on methanotrophs and their resilience to sulfide exposure is not well understood, highlighting the need for targeted research. Investigating the inhibitory thresholds and physiological response of methanotrophs is crucial for developing accurate models of methane emissions and managing carbon and sulfur cycles in impacted ecosystems (Lenstra et al., 2023).
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