Streptococcus ruminicola sp. nov., new species of the Streptococcus bovis/Streptococcus equinus complex (SBSEC) isolated from the rumen of Korean domestic ruminants.

A total of three Gram-positive, and oxidase and catalase-negative facultative anaerobic non-motile bacteria were isolated from the rumen fluid of cows and goats and these strains were designated CNU_G2, CNU_77-61, and CNU_G3. They grew at 20-45 °C, pH 6.5-7, and 0-6.5% NaCl (w/v). The G + C contents (%) of the three isolates were 37.9, 37.8 and 37.8, respectively. Phylogenomic analysis indicated that these strains were distinct from other Streptococcus species. The average nucleotide identity between the isolates and the closest strain S. infantarius subsp. infantarius ATCC BAA-102 was 94.0-94.5%, while the digital DNA-DNA hybridization (dDDH) values between the isolates and the aforementioned related strain were 58.2-61.4%, respectively. Fatty acid analysis revealed higher proportions of C (> 28%) in all three isolates, while the proportion of C was higher in CNU_G2 (25.8%); however, it was less than 12% in all the representing strains used in the study. The C composition of strains CNU_77-61 (22.1%) and CNU_G3 (24.1%) was higher than that of type strains of CNU_G2 (8.1%). Based on the morphological, biochemical, and molecular phylogenetic features of the three novel isolates, they represent a novel species of the genus Streptococcus, for which we propose as Streptococcus ruminicola sp. nov. The type strain is CNU_G2 (= KCTC 43308 = GDMCC 1.2785).