gen. nov., sp. nov., a novel representative of the phylum and proposal of fam. nov., ord. nov. and class. nov.

is widespread and ecologically important in various anoxic environments. However, the portion of culturable bacteria within this phylum is quite low and, in fact, there is only one currently described species. In this study, a novel anaerobic, non-motile, coccoid, Gram-stain-negative bacterial strain, designated S-5007, was isolated from surface marine sediment. The 16S rRNA gene sequence was found to have very low 16S rRNA gene sequence similarity to the nearest known type strain, L21-Fru-AB (84.9 %). The taxonomic position of the novel isolate was investigated using a polyphasic approach and comparative genomic analysis. Phylogenetic analyses based on 16S rRNA genes and genomes indicated that strain S-5007 branched within the radiation of the phylum . Different from the type strain, strain S-5007 can grow under microaerobic conditions, and the genomes of strain S-5007 and the other strains in its branch have many more antioxidant-related genes. Meanwhile, other different metabolic features deduced from genome analysis supported the separate evolution of the proposed class (strain S-5007 branch) and L21-Fru-AB. Based on phylogenetic and phenotypic characterization studies, gen. nov., sp. nov. is proposed with S-5007 (=MCCC 1H00402=KCTC 15876) as the type strain, as the first representative of novel taxa, ord. nov., fam. nov. in class. nov.