Description of Streptococcus dentalis sp. nov., Streptococcus gingivalis sp. nov., and Streptococcus lingualis sp. nov., Isolated from Human Oral Cavities.

We isolated three novel strains, S1 ^T , S2 ^T , and S5 ^T , from human oral cavities and identified them as distinct novel species. All these strains are facultatively anaerobic, Gram-stain-positive, and non-flagellated bacteria. Their optimal growth conditions for these strains were observed in Columbia broth (CB) at 37 °C, pH 7.0, and in the absence of NaCl. Phylogenetic analyses, employing the 16S rRNA gene and whole-genome sequencing, confirmed that all three strains belong to the genus Streptococcus. The 16S rRNA gene sequences of strains S1 ^T , S2 ^T , and S5 ^T showed the highest similarities to Streptococcus parasanguinis, 98.57%, 99.05%, and 99.05%, respectively, and the orthologous average nucleotide identity (OrthoANI) values between the three strains and S. parasanguinis were 93.82%, 93.67%, and 94.04%, respectively. The pairwise OrthoANI values between the novel strains were 94.37% (S1 ^T -S2 ^T ), 95.03% (S2 ^T -S5 ^T ), and 94.71% (S1 ^T -S5 ^T ). All strains had C _20:1 ω9c and summed feature 8 (C _18:1 ω7c and/or C _18:1 ω6c) as major cellular fatty acids. Additionally, diphosphatidylglycerol (DPG) and hydroxyphosphatidylethanolamine (OH-PE) were identified as major polar lipids. Menaquinone was undetected in all strains. The results from the phylogenetic, phenotypic, chemotaxonomic, and genotypic analyses collectively indicated that strains S1 ^T , S2 ^T , and S5 ^T represent three distinct novel species within the genus Streptococcus, and we propose the names Streptococcus dentalis sp. nov. for strain S1 ^T (= KCTC 21234 ^T  = JCM 36526 ^T ), Streptococcus gingivalis sp. nov. for strain S2 ^T (= KCTC 21235 ^T  = JCM 36527 ^T ), and Streptococcus lingualis sp. nov. for strain S5 ^T (= KCTC 21236 ^T  = JCM 36528 ^T ).
Competing Interests: Declarations. Conflict of Interest: The authors declare that there are no conflicts of interest. Ethical Statements: This study was conducted following the IRB regulations at Kyung Hee University (KHSIRB-21–533).
(© 2024. The Author(s), under exclusive licence to Microbiological Society of Korea.)