Streptococcus bovismuti sp. nov., a novel species isolated from yak milk

In this study, a novel bacterial strain, IMAU11622^T, was isolated from the milk of yaks in Yunnan Province, China. This strain was characterized as a Gram-positive, catalase-negative, α-haemolytic, coccus-shaped bacterium belonging to the genus Streptococcus (S.). The strain IMAU11622^T belongs to the mitis-suis clade, the pneumoniae subclade, of the genus Streptococcus. Phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that the strain IMAU11622^T shared high similarity with S. mitis ATCC 49456^T and S. thalassemiae Marseille Q2617^T (99.7%), S. pseudopneumoniae CCUG 49455^T (99.5%), S. pneumoniae ATCC 33400^T (99.2%), S. oralis subsp. oralis ATCC 35037^T and S. oralis subsp. dentisani Str. 7747^T (99.1%) and S. infantis ATCC 700779^T (99.0%). Phylogenetic analysis of 7 housekeeping gene (rpoB, gyrB, ppaC, sodA, tuf, pflA and guaA) sequences and a phylogenetic tree based on 158 core genes further differentiated the strain IMAU11622^T, which was distinct from the closely related strains. The highest average nucleotide identity and digital DNA-DNA hybridization values for strain IMAU11622^T were 94.6 and 55.6%, respectively, in comparison with S. mitis ATCC 49456^T. The draft genome size of strain IMAU11622^T was 1,973,043 bp, and the DNA G+C content of the type strain was 40.0%. The major cellular fatty acids were C_16 : 0, summed feature 3 (containing C_16 : 1  ω7c/or C_16 : 1  ω6c), summed feature 8 (containing C_18 : 1  ω7c and C_18 : 1  ω6c) and C_14 : 0. The strain IMAU11622^T exhibited growth at a temperature ranging 25-45 °C (with an optimum growth temperature of 37 °C), a pH range of 5.0-8.0 (with an optimum growth pH of 7.0) and tolerance up to 2% NaCl. Based on polyphasic taxonomic characterization, the strain IMAU11622^T is a novel species within the genus Streptococcus, for which the name Streptococcus bovismuti sp. nov. is proposed, with the type strain IMAU11622^T (=JCM 37064^T=CGMCC 1.64733^T=GDMCC 1.4462^T).