Three strictly anaerobic, Gram-positive, non-spore-forming, rod-shaped, motile bacteria, designated strains ACB1(T), ACB7(T) and ACB8, were isolated from human subgingival dental plaque. All strains required yeast extract for growth. Strains ACB1(T) and ACB8 were able to grow on glucose, lactose, maltose, maltodextrin and raffinose; strain ACB7(T) grew weakly on sucrose only. The growth temperature range was 30-42 °C with optimum growth at 37 °C. Major metabolic fermentation end products of strain ACB1(T) were acetate and lactate; the only product of strains ACB7(T) and ACB8 was acetate. Major fatty acids of strain ACB1(T) were C(14 : 0), C(16 : 0), C(16 : 1)ω7c dimethyl aldehyde (DMA) and C(18 : 1)ω7c DMA. Major fatty acids of strain ACB7(T) were C(12 : 0), C(14 : 0), C(16 : 0), C(16 : 1)ω7c and C(16 : 1)ω7c DMA. The hydrolysate of the peptidoglycan contained meso-diaminopimelic acid, indicating peptidoglycan type A1γ. Genomic DNA G+C content varied from 42 to 43.3% between strains. According to 16S rRNA gene sequence phylogeny, strains ACB1(T), ACB8 and ACB7(T) formed two separate branches within the genus Oribacterium, with 98.1-98.6% sequence similarity to the type strain of the type species, Oribacterium sinus. Predicted DNA-DNA hybridization values between strains ACB1(T), ACB8, ACB7(T) and O. sinus F0268 were <70%. Based on distinct genotypic and phenotypic characteristics, strains ACB1(T) and ACB8, and strain ACB7(T) are considered to represent two distinct species of the genus Oribacterium, for which the names Oribacterium parvum sp. nov. and Oribacterium asaccharolyticum sp. nov. are proposed. The type strains are ACB1(T) ( = DSM 24637(T) = HM-481(T) = ATCC BAA-2638(T)) and ACB7(T) ( = DSM 24638(T) = HM-482(T) = ATCC BAA-2639(T)), respectively.
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