An anaerobic isolate, strain AT7, was cultivated from a stool sample of a morbidly obese French woman using a microbial culturomics approach. The 16S rRNA gene sequence analysis showed that strain AT7 exhibited 96% nucleotide sequence similarity with Ruminococcus torques strain JCM 6553 (= ATCC 27756 = VPI B2-51), currently the closest related species with a validly published name. The strain was observed to be a Gram-stain positive, non-motile, asporogenous and coccobacillary-shaped bacterium. It was found to be catalase positive and oxidase negative. Its major fatty acids were identified as C (54%) and C (30%). The draft genome of strain AT7 is 3,069,882 bp long with 42.4% G+C content. 2925 genes were predicted, including 2867 protein-coding genes and 58 RNAs. Based on phenotypic, biochemical, phylogenetic and genomic evidence, we propose the creation of the new genus Mediterraneibacter and species, Mediterraneibacter massiliensis, that contains strain AT7 (= CSUR P2086 = DSM 100837), and the reclassification of Ruminococcus faecis, Ruminococcus lactaris, Ruminococcus torques, Ruminococcus gnavus, Clostridium glycyrrhizinilyticum as Mediterraneibacter faecis comb. nov., with type strain Eg2 (= KCTC 5757 = JCM15917), Mediterraneibacter lactaris comb. nov., with type strain ATCC 29176 (= VPI X6-29), Mediterraneibacter torques comb. nov., with type strain ATCC 27756 (= VPI B2-51), Mediterraneibacter gnavus comb. nov., with type strain ATCC 29149T (= VPI C7-9T) and Mediterraneibacter glycyrrhizinilyticus comb. nov., with type strain ZM35 (= JCM 13368 = DSM 17593), respectively.