## 3 Results and Discussion
### Phylogenetics of MAGs and Their Abundance in the PSD and AnMBR
The closest genome affiliated with MAG11 was _Methanospirillum humugatei_ JF-1, whereas the genome of MAG220 was affiliated with _Methanosaeta harundinacea_ 6 Ac. During the degradation of complex organic matter to carbon dioxide and methane in anaerobic environments, _M. humugatei_ uses hydrogen or formate to produce methane, which are produced by other syntrophic microbes [56]. _M. harundinacea_ is an acetate-scavenging methanogen isolated from a upflow anaerobic sludge blanket reactor [57]. A _Bacteroidetes_ endosymbiont of _Geopenphigus_ sp. exhibited the highest relationship with MAG158, MAG217, MAG228, MAG42, and MAG83. _Prolixibacteraceae_ bacterium XSD2, _Fusobacteriaceae_ bacterium, _Nitrospirae_ bacterium HCH-1, and _Desulfovibrio cuneatus_ DSM 11,391 were most similar with the genomes of MAG59, MAG142, MAG161, and MAG68, respectively. _D. cuneatus_ is a psychrotolerant sulfate-reducing bacterium isolated from an oxic freshwater sediment [58]. In addition, MAG55, MAG100, MAG74, MAG200, and MAG159 showed the highest similarity with _Sulfurovum_ sp. NBC37-1, _Succinatimus hippei_ YIT 12066, _Aminophilus circumscriptus_ DSM 16,581, _Synergistaceae_ bacterium, and _Succinispira mobilis_ DSM 6222, respectively. _Sulfurovum_ sp. NBC37-1 is a chemolithoautotroph deep-sea _Epsilonproteobacteria_ that obtains energy through mesophilic hydrogen- and sulfur-oxidation [59]. _S. hippei_ YIT 12066T was isolated from human feces, and the growth of _S. hippei_ YIT 12,066 T depends on CO\({}_{2}\) or bicarbonate [60]. _A. circumscriptus_ is an anaerobic amino-acid-degrading bacterium from an upflow anaerobic sludge reactor [61], and _S. mobilis_ was proven to be a succinate-decarboxylolating anaerobic bacterium in a mixed culture growing with glycolate [62]. To estimate the relative abundance of the MAGs represented in the PSD and AnMBR, all the quality-filtered reads from each sample were aligned to the contigs from each MAG with Bowtie2 software. As shown in Figure 3, the relative abundance of the MAGs exhibited a large divergence between the PSD and AnMBR. For example, the highest coverage was observed in MAG16 (affiliated with _Methanobacterium_ sp., with 5.27% reads mapped on the corresponding contigs in PSD), followed by MAG200 (affiliated with _Synergistaceae_ bacterium, 2.79%), MAG13 (affiliated with _Methanobacterium_ sp. ), MAG74 (affiliated with _A. circumscriptus_) and MAG220 (affiliated with _M. concili_), which were the other predominant species in the PSD, with abundances of 1.42%, 1.18%, and 0.96%, respectively. In the AnMBR metagenome, MAG83 (classified as _Bacteroidetes_ bacterium), MAG200 (_Synergistaceae_ bacterium), MAG217 (_Bacteroidetes_ bacterium), MAG42 (_Bacteroidales_ bacterium), and MAG59 (_Prolixibucteraceae_ bacterium) were the most abundant species, with relative abundances of 4.74%, 2.93%, 2.85%, 1.59%, and 1.36%, respectively (Figure 3). _Methanobacteriaceae_ is capable of directly converting gaseous hydrogen and carbon dioxide into methane [63], whereas microorganisms belonging to _Synergistaceae_ family (_Aminobacterium thunnarium_, _Aminobacterium_, and _Aminivibrio pyruvatophilus_) are certified as syntrophic acetate oxidizers [64, 65]. This result may also derive from the functional difference between the PSD and AnMBR in the DWTS, in which wastewater was solid-liquid separated, and organic matter was degraded in the AnMBR, followed by methanogenesis in the sludge of PSD bioreactors.