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_S^T, and coccobacilli, strain 25CYCFAH16^T, were isolated from faecal samples of healthy Japanese volunteers. Strain 21CYCFAH17_S^T showed the highest 16S rRNA gene sequence similarity to <i>Hominimerdicola aceti</i> DSM 102216^T (95.3%) and <i>Ruminococcus albus</i> 7^T (93.2%). Strain 25CYCFAH16^T showed the highest 16S rRNA gene sequence similarity to <i>Ruminococcus champanellensis</i> 18P13^T (94.3%) and <i>Ruminococcus flavefaciens</i> ATCC 19208^T (93.9%). The 16S rRNA gene phylogenetic analysis showed that strain 25CYCFAH16^T, <i>R. champanellensis</i> JCM 17042^T, <i>R. flavefaciens</i> ATCC 19208^T and <i>Ruminococcus callidus</i> ATCC 27760^T formed a monophyletic cluster. Strain 21CYCFAH17_S^T, '<i>Ruminococcus bicirculans</i>' 80/3^T (<i>H. aceti</i> 80/3^T) and <i>R. albus</i> JCM 14654^T 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_S^T and 25CYCFAH16^T (<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 <i>Hominimerdicola</i>, including strain 21CYCFAH17_S^T, exhibited α-arabinosidase activity, whereas strain 25CYCFAH16^T and other members of the genus <i>Ruminococcus</i> did not. Moreover, differences in cellular fatty acid composition were observed between the genera, with members of the genus <i>Hominimerdicola</i> containing C_14:0, C_16:0, iso-C_14:0 and iso-C_13:0 3-hydroxyl as characteristic fatty acids, whereas members of the genus <i>Ruminococcus</i> were characterized by iso-C_15:0, anteiso-C_17:0 and unknown 16:1 <i>ω</i>7<i>c</i> dimethyl acetal. These results indicate that isolates 21CYCFAH17_S^T and 25CYCFAH16^T represent novel species of the genera <i>Hominimerdicola</i> and <i>Ruminococcus</i>, respectively. Based on the collected data, strain 21CYCFAH17_S^T was identified as a novel species in the genus <i>Hominimerdicola</i>, for which the name <i>Hominimerdicola intestinalis</i> sp. nov. is proposed. In addition, strain 25CYCFAH16^T was identified as a novel species within the genus <i>Ruminococcus</i>, for which the name <i>Ruminococcus sporogenes</i> sp. nov. is proposed. The type strain of <i>H. intestinalis</i> is 21CYCFAH17_S^T (=JCM 36633^T=DSM 118075^T), and the type strain of <i>R. sporogenes</i> is 25CYCFAH16^T (=JCM 36793^T=DSM 118006^T). Additionally, <i>R. albus</i> is transferred to the genus <i>Hominimerdicola</i> as <i>Hominimerdicola alba</i> comb. nov.