Hominimerdicola intestinalis sp. nov. and Ruminococcus sporogenes sp. nov., isolated from human faeces, and reclassification of Ruminococcus albus Hungate 1957 as Hominimerdicola alba comb. nov.

Obligately anaerobic, Gram-stain-positive staphylococci, strain 21CYCFAH17_ST, and coccobacilli, strain 25CYCFAH16T, were isolated from faecal samples of healthy Japanese volunteers. Strain 21CYCFAH17_ST showed the highest 16S rRNA gene sequence similarity to Hominimerdicola aceti DSM 102216T (95.3%) and Ruminococcus albus 7T (93.2%). Strain 25CYCFAH16T showed the highest 16S rRNA gene sequence similarity to Ruminococcus champanellensis 18P13T (94.3%) and Ruminococcus flavefaciens ATCC 19208T (93.9%). The 16S rRNA gene phylogenetic analysis showed that strain 25CYCFAH16T, R. champanellensis JCM 17042T, R. flavefaciens ATCC 19208T and Ruminococcus callidus ATCC 27760T formed a monophyletic cluster. Strain 21CYCFAH17_ST, 'Ruminococcus bicirculans' 80/3T (H. aceti 80/3T) and R. albus JCM 14654T were located near the cluster, which is consistent with the genome-based analyses. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of strains 21CYCFAH17_ST and 25CYCFAH16T (<37% dDDH and <73% ANI) were below the threshold values for species delineation when compared with their closest relatives. In addition, phenotypic characteristics further differentiated the two genera: members of the genus Hominimerdicola, including strain 21CYCFAH17_ST, exhibited α-arabinosidase activity, whereas strain 25CYCFAH16T and other members of the genus Ruminococcus did not. Moreover, differences in cellular fatty acid composition were observed between the genera, with members of the genus Hominimerdicola containing C14:0, C16:0, iso-C14:0 and iso-C13:0 3-hydroxyl as characteristic fatty acids, whereas members of the genus Ruminococcus were characterized by iso-C15:0, anteiso-C17:0 and unknown 16:1 ω7c dimethyl acetal. These results indicate that isolates 21CYCFAH17_ST and 25CYCFAH16T represent novel species of the genera Hominimerdicola and Ruminococcus, respectively. Based on the collected data, strain 21CYCFAH17_ST was identified as a novel species in the genus Hominimerdicola, for which the name Hominimerdicola intestinalis sp. nov. is proposed. In addition, strain 25CYCFAH16T was identified as a novel species within the genus Ruminococcus, for which the name Ruminococcus sporogenes sp. nov. is proposed. The type strain of H. intestinalis is 21CYCFAH17_ST (=JCM 36633T=DSM 118075T), and the type strain of R. sporogenes is 25CYCFAH16T (=JCM 36793T=DSM 118006T). Additionally, R. albus is transferred to the genus Hominimerdicola as Hominimerdicola alba comb. nov.