Taxogenomic investigation of members in the Streptomyces glaucosporus group and reclassification of Streptomyces chitinivorans, Streptomyces pini and Streptomyces atacamensis

Members in the Streptomyces glaucosporus group were limited to only four species by 2006, but recently, new species belonging to the group have been proposed after Streptomyces radiopugnans was proposed in 2007. Nowadays, 13 species are published as validly published and correct names. In this study, taxonomic positions of the members were re-investigated by analysing 16S rRNA gene and whole-genome sequences and comparing phenotypes. In pairwise 16S rRNA gene sequence comparisons, type strains of Streptomyces chitinivorans , Streptomyces pini and Streptomyces atacamensis were the most closely related to those of Streptomyces fenghuangensis (99.9%), Streptomyces mangrovi (99.7%) and S. radiopugnans (99.2%), respectively. Digital DNA–DNA hybridization value and average nucleotide identity based on MUMmer between S. chitinivorans KCTC 29696 T and S. fenghuangensis NRRL B 24801 T were 86.8% and 98.6%, respectively; those between S. pini PL19 T and S. mangrovi DSM 42113 T were 82.7% and 98.1%; those between S. atacamensis KACC 15492 T and S. radiopugnans CGMCC 4.3519 T were 87.6% and 98.7%. These overall genome related indices were above the thresholds for species delineation. Significant phenotypic differences were not observed in each pair. According to nomenclatural priorities, S. chitinivorans Ray et al . 2016, S. pini Madhaiyan et al . 2016 and S. atacamensis Santhanam et al . 2012 were reclassified as later heterotypic synonyms of S. fenghuangensis Zhu et al . 2011, S. mangrovi Wang et al . 2015 and S. radiopugnans Mao et al . 2007, respectively. Type-I polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) gene clusters were well conserved between synonymous species although type strains of S. chitinivorans and S. fenghuangensis did not harbour typical PKS and NRPS gene clusters. Repertoires of major PKS and NRPS gene clusters are likely specific in each species if the species are appropriately classified.