Actinomycete strains OM-6519T and K04-0144T produce the bioactive compounds lactacystin and cyslabdan, respectively.Here, the taxonomic positions of these two strains were determined. The morphological and chemical features of strains OM-6519T and K04-0144T indicated that they belonged to the genus Streptomyces. Strain OM-6519T showed the highest 16S rRNA gene sequence similarities with Streptomyces xanthocidicus NBRC 13469T (99.7%), Streptomyces chrysomallus subsp. fumigatus NBRC 15394T (99.6%) and Streptomyces aburaviensis NRRL B-2218T (99.5%). However, the DNA-DNA relatedness values between strain OM-6519T and the three related strains were below 70%. Strain K04-0144T showed the highest 16S rRNA gene sequence similarities with Streptomyces corchorusii NBRC 13032T (99.4%), Streptomyces olivaceoviridis NBRC 15394T (99.4%) and Streptomyces canarius NRRL B-2218T (99.3%). However, the DNA-DNA relatedness values between strain K04-0144T and the three related strains were also below 70%. Based on morphological, cultural and physiological characteristics and DNA-DNA relatedness data, strains OM-6519T and K04-0144T should be classified as new species of the genus Streptomyces, for which the names Streptomyces lactacystinicus sp. nov. and Streptomyces cyslabdanicus sp. nov. are proposed. The type strain of S. lactacystinicus is OM-6519T (=NBRC 110082T, DSM 43136T). The type strain of S. cyslabdanicus is K04-0144T (=NBRC 110081T, DSM 42135T).
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