Representatives of the Synergistaceae family, taxonomic description and genome sequence of Caenicola nitritireducens gen nov., sp. nov., a novel fermenting and amino-acid degrading bacterium isolated from a municipal anaerobic digester sludge

Members of the phylum Synergistota are important but understudied components of microbial communities during anaerobic digestion. In this study, their diversity was assessed in full-scale anaerobic digester sludge samples from Marrakesh wastewater treatment plant (Morocco), using 16S rRNA gene community profiling, as well as targeted isolation, physiological characterization, and genome sequencing of novel Synergistaceae isolates. The 16S rRNA gene analysis identified 23 operational taxonomic units (OTUs) belonging to the family of Synergistaceae, representing 8.8 % of the total microbial community. 17 of these OTUs belonged to previously uncultured taxa. A dominant OTU19, presumably a new representative of the family of Synergistaceae was isolated in pure culture (strain DS-S4^T) and subjected to both culture- and genome-based characterizations. Phylogenetic analysis revealed that strain DZ-S4^T was related to Cloacibacillus porcorum CL-84^T and Cloacibacillus evryensis 158^T but with low sequence similarity of 89.94 % and 88.60 %, respectively. Based on genome relatedness, including Average Nucleotide Identity (ANI) and Amino Acid Identity (AAI), strain DZ-S4^T is considered to represent a novel genus for which the name Caenicola gen.nov is proposed. Moreover, several phenotypic and eco-physiological properties differentiated the novel isolate from its related species, indicating that the strain represents a new species for which the name Caenicola nitritireducens sp. nov. is proposed, with strain DZ-S4^T (=DSM 104940^T = JCM 31897^T) being the type strain. Additionally, this study investigates the ecological role of strain DZ-S4^T, specifically the protein degradation, the bioconversion of carbohydrates, and the nitrite reduction during anaerobic digestion.