Proposal of Streptomyces janthinus (Artamonova and Krassilnikov 1960) Pridham 1970 (Approved Lists 1980) as a later heterotypic synonym of Streptomyces violaceus (Rossi Doria 1891) Waksman 1953 (Approved Lists 1980) and an emended description of Streptomyces violaceus.

The taxonomic relationship between Streptomyces janthinus and Streptomyces violaceus was re-evaluated using comparative genome analysis. The 16S rRNA gene sequence analysis indicated that the type strains of S. janthinus and S. violaceus shared 100% sequence similarity. Phylogenetic trees based on 16S rRNA gene sequences indicated that S. janthinus JCM 4387^T was clustered together with S. violaceus CGMCC 4.1456^T. These results suggested that S. janthinus JCM 4387^T was most closely related to S. violaceus CGMCC 4.1456^T. The phylogenomic tree also supported this result. The average nt identity (ANI) and dDDH values between these two strains were 97.89% and 81.0%, respectively, well more than the 96.7% ANI and 70% dDDH threshold values for Streptomyces species delineation, confirming that S. janthinus JCM 4387^T and S. violaceus CGMCC 4.1456^T belong to the same genomic species. In addition, a comprehensive comparison of phenotypic, chemotaxonomic and genomic characteristics also supported this conclusion. According to all these results and Rule 42 of the Bacteriological Code, we propose S. janthinus (Artamonova and Krassilnikov 1960) Pridham 1970 (Approved Lists 1980) as a later heterotypic synonym of S. violaceus (Rossi Doria 1891) Waksman 1953 (Approved Lists 1980).