46 Chapter 2 ANME archaea are key players in anaerobic methane removal in marine sediment ecosystems ranging from coastal zones to the deep sea (Aromokeye et al., 2020; Bhattarai et al., 2017; Gründger et al., 2019; Pernthaler et al., 2008; Stokke et al., 2012). Phylogenetically, ANME form three major clades: ANME-1, ANME2, and ANME-3, assigned a putative nomenclature at family and genus level (Chadwick et al., 2022), to which we refer in this section. ANME-1, in the order Methanophagales, comprises the family Methanophagaceae with at least 6 genera, and are present at a broad range of temperatures, from 2 to 100°C (Bhattarai et al., 2019). Members of this clade have been implicated in both methanogenesis and methane oxidation in estuarine sediments (Kevorkian et al., 2021). ANME-2, in the order Methanosarcinales, comprises the family Methanocomedenaceae, with two genera, “Ca. Methanocomedens” (ANME-2a) and “Ca. Methanomarinus” (ANME2b), the family Methanogasteraceae (ANME-2c), and the family Methanoperedenaceae (ANME-2d). Members of this clade inhabit a narrower range of temperatures (4 to 20°C) (Bhattarai et al., 2019). Finally, ANME-3, also in the order Methanosarcinales, comprises the family Methanosarcinaceae with the genus “Ca. Methanovorans”, and has been reported in colder temperatures (-1 to 17°C) (Bhattarai et al., 2019). While ANME-1, ANME-2 and ANME-3 have been implicated in sulfate-dependent anaerobic oxidation of methane (S-AOM) in consortia with a syntrophic sulfatereducing partner (Bhattarai et al., 2019; Boetius et al., 2000), ANME-2d can independently perform nitrate-dependent, iron-dependent and manganesedependent anaerobic oxidation of methane (N-AOM, Fe-AOM, and Mn-AOM, respectively)(Cai et al., 2018; Ettwig et al., 2016; Haroon et al., 2013; Leu et al., 2020a). ANME-2a were enriched in Fe-AOM incubations with sediments of the North Sea (Aromokeye et al., 2020) and their 16S rRNA gene-based abundance correlated to methane and Fe concentrations in sediments of the Bothnian Sea (Rasigraf et al., 2020). Moreover, ANME-2a, 2b, 2c, 2d and ANME-3 genomes have genes predicted to encode multiheme c-type cytochromes potentially implicated in extracellular electron transfer and Fe reduction (Chadwick et al., 2022), suggesting that multiple ANME groups might perform metal-AOM. The Baltic Sea is highly impacted by eutrophication (Conley et al., 2011; Murray et al., 2019) and has been proposed as a model marine ecosystem indicative of future global changes related to anthropogenic impacts such as oxygen depletion
RkJQdWJsaXNoZXIy MTk4NDMw