34 Chapter 1 ON “Ca. Methanoperedens” AS A METHANOTROPHIC STUDY MODEL “Ca. Methanoperedens” has demonstrated a highly versatile metabolism, allowing it to thrive in various ecosystems, including freshwater anoxic environments (e.g. wetland) and soils (e.g. peat) and groundwater systems. It has also been reported in marine metagenomes, although with reduced coverage compared to marine ANME (Chapter 7) (Figure 3). This suggests that “Ca. Methanoperedens” serves as a widespread methane biofilter across diverse natural ecosystems, making it a favorable subject for study. Bioreactors have been successfully used to enrich this environmentally relevant genus (Figure 3). Over the past decade, distinct cultures have been successfully obtained under conditions with nitrate, manganese, and iron oxides. In nitrate bioreactor enrichments, “Ca. Methanoperedens” pairs with nitrite scavengers. During nitrate/nitrite-dependent anaerobic methane oxidation (N-DAMO), “Ca. Methanoperedens” collaborates with methanotrophic nitritescavenging partners from the genus “Ca. Methylomirabilis” (Figure 3) (Chapter 5). Furthermore, “Ca. Methanoperedens” works with anaerobic ammoniumoxidizing (anammox) bacteria as nitrite scavengers, facilitating dissimilatory nitrate reduction to ammonium and providing ammonium in exchange for nitrite removal by anammox bacteria (Chapter 4). Other nitrite scavengers may include autotrophic or heterotrophic denitrifiers (Chapter 6). The ability of “Ca. Methanoperedens” to use various electron acceptors highlights the resilience of the methane biofilter, but this system remains sensitive to environmental stressors. Lateral gene transfer was emphasized as a way of Methanoperedenaceae to expand the presence of e.g. multiheme c-type cytochrome (MHCs) (Leu et al., 2020b). Recent findings have revealed that the presence of mobile genetic elements (MGEs) associated to “Ca. Methanoperedens” could enhance its known metabolic versatility. These elements have been linked to plasmids and viruses in bioreactor systems, as well as to novel extrachromosomal elements known as Borgs found in environmental soil samples (Al-Shayeb et al., 2022; Schoelmerich et al., 2022).
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