Sharpea azabuensis gen. nov., sp. nov., a Grampositive, strictly anaerobic bacterium isolated from the faeces of thoroughbred horses

Four bacterial strains, designated ST18^T, HM244, HM250 and DI49, were isolated from the fresh faeces of four thoroughbred horses in Japan. Cells were Gram-positive, strictly anaerobic, catalase-negative, non-spore-forming, non-motile rods that occurred in chains. They were placed in the same subcluster based on 16S rRNA gene sequence analysis, phenotypic characteristics and levels of DNA-DNA relatedness. Their DNA G+C content ranged from 36 to 38 mol%. Lactobacillus catenaformis, Lactobacillus vitulinus and Catenibacterium mitsuokai belong to cluster XVII of the Clostridium subphylum. Strain ST18T was most closely related to L. catenaformis ATCC 25536^T in the phylogenetic tree, but these strains shared only 89.9% (1336/1486 bp) 16S rRNA gene sequence similarity. L. catenaformis, L. vitulinus and C. mitsuokai are homofermentative bacteria, whereas ST18^T produced CO₂ from glucose. Whereas the cell-wall peptidoglycan type of L. catenaformis and L. vitulinus was L-Lys-L-Ala₃, that of C. mitsuokai and the subgroup represented by ST18^T was A1γ (L-Ala-D-Glu-meso-diaminopimelic acid). On the basis of 16S rRNA gene sequence divergence of more than 10% from L. catenaformis as well as phenotypic characteristics, strains ST18^T, HM244, HM250 and DI49 are considered to represent a novel species of a new genus belonging to the Clostridium subphylum cluster XVII, for which the name Sharpea azabuensis gen. nov., sp. nov. is proposed. The type strain of Sharpea azabuensis is ST18^T (=JCM 14210^T =DSM 18934^T).