Taxonomic characterization of Mogibacterium diversum sp nov and Mogibacterium neglectum sp nov., isolated from human oral cavities

Novel isolates, strains HM-7, HM-6, HH-31, P9a-h(T) and UJB13-d, which were isolated from tongue plaque and necrotic dental pulp, were studied taxonomically and phylogenetically. These organisms were anaerobic, non-spore-forming, Gram-positive, rod-shaped bacteria that were inert in most of the conventional biochemical tests and phenotypically resemble Mogibacterium species or asaccharolytic Eubacterium species. The G+C contents of the DNAs from the novel isolates ranged from 41 to 42 mol %. DNA-DNA hybridization studies demonstrated that these strains might be assigned to the genus Mogibacterium but not to the previously described species. It was also apparent that strain HM-7 belonged to the same species as strains HM-6 and HH-31, and that strains P9a-h(T) and UJIB13-d belonged to a second species. The levels of DNA-DNA relatedness to asaccharolytic Eubacterium species, including Eubacterium brachy, Eubacterium nodatum, Eubacterium saphenum and the more recently proposed Eubacterium minutum and Eubacterium exiguum (reclassified as Slackia exigua), are less than 2 %. The results of 16S rDNA sequence comparisons revealed that these organisms represent novel lineages distinct from all previously described species of Gram-positive, rod-shaped bacteria. On the basis of phenotypic characteristics, DNA-DNA hybridization data and phylogenetic analysis with 16S rRNA gene sequence data, new species are proposed, namely Mogibacterium diversum (for strains HM-7,HM-6 and HH-31) and Mogibacterium neglectum (for strains P9a-h(T) and UJB13-d). HM-7(T) (= ATCC 700923(T) = JCM 11205(T)) is the type strain of the former and P9a-h(T) (= ATCC 700924(T) = JCM 11204(T)) is the type strain for the latter.