Genomic Characterization and Comparative Analysis of Streptococcus zhangguiae sp. nov. Isolated from the Respiratory Tract of Marmota Himalayana.

Two Gram-stain-positive, oxidase-negative, non-motile, facultative anaerobic, α-hemolytic, coccus-shaped bacteria (zg-86^T and zg-70) were isolated from the respiratory tracts of marmots (Marmota Himalayana) on the Qinghai-Tibet Plateau of China. Phylogenetic analysis of the 16S rRNA gene and 545 core genes revealed that these two strains belong to the Streptococcus genus. These strains were most closely related to Streptococcus respiraculi HTS25^T, Streptococcus cuniculi CCUG 65085^T, and Streptococcus marmotae HTS5^T. The average nucleotide identity (ANI) and digital DNA‒DNA hybridization (dDDH) were below the threshold for species delineation. The predominant cellular fatty acids (CFAs) in this novel species were C_16:0, C_18:0, and C_18:1ω9c, whereas the primary polar lipids were phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and an unknown phosphoglycolipid (PGL). The optimal growth conditions for the strains were 37 °C, pH 7.0, and 0.5% (w/v) NaCl on brain-heart infusion (BHI) agar supplemented with 5% defibrinated sheep blood. Comparative genomics analyses revealed the potential pathogenicity of strain zg-86^T through comparisons with suis subclade strains in terms of virulence factors, pathogen-host interactions (PHIs) and mobile genetic factors (MGEs). Based on the phenotypic characteristics and phylogenetic analyses, we propose that these two isolates represent novel species in the genus Streptococcus, for which the names Streptococcus zhangguiae sp. nov. (the type strain zg-86^T=GDMCC 1.1758^T=JCM 34273^T) is proposed.