Genomic characterization of a potentially novel Streptococcus species producing exopolysaccharide.

Human oral streptococci, particularly the mitis group, often dwell in the upper respiratory tracts, oral mucosa, and tooth surfaces of healthy individuals. In this work, an α-hemolytic strain, designated LQJ-218, was isolated from the human oral cavity and evaluated for its ability to produce exopolysaccharides. Phylogenetic analysis based on 16S rRNA gene sequences showed that this strain is a potentially novel species belonging to the mitis group streptococci. Whole-genome sequence-based analysis indicated that the genome sequence of Streptococcus sp. LQJ-218 was 1,935,194 bp in length, with a mol% G + C content of 40.0, and contained 1897 coding DNA sequences and 91 RNA genes. Furthermore, four biosynthetic gene clusters relevant to exopolysaccharide production were identified in the genome. Both digital DNA-DNA hybridization (yielding a value of 56.60% between strain LQJ-218 and its nearest relative S. mitis) and average nucleotide identity analysis (revealing 91.29% identity of LQJ-218 with its nearest relative S. mitis) suggested that strain LQJ-218 should be classified as a novel Streptococcus species. This potentially novel strain may possess great potential for contributing to the development of new exopolysaccharides. The present study provides valuable genetic information that may be useful in comparative genomics and biotechnological applications.