Description of Streptomyces siderophoricus sp. nov., a promising nocardamine-producing species isolated from the rhizosphere soil of Mangifera indica

An actinomycete, designated strain CH9-7(T), was isolated from the rhizosphere soil of Mangifera indica. The morphological and chemotaxonomic properties, such as the production of spiral spore chains and the presence of LL-diaminopimelic acid in the peptidoglycan, showed that it belongs to the genus Streptomyces. Based on the 16S rRNA gene analysis, it was confirmed that strain CH9-7(T) was a member of the genus Streptomyces and revealed 99.9% 16S rRNA gene sequence similarity to its closest relative strains, Streptomyces lydicus NBRC 13058 (T) and Streptomyces chattanoogensis NBRC 12754 (T). Although the strain showed high 16S rRNA gene sequence similarity values, however, genome relatedness indexes exhibited that the average nucleotide identity based on the MUMmer (ANIm) algorithm, the average amino acid identity (AAI), and the digital DNA-DNA hybridization values between strain CH9-7(T) and its closest phylogenomic relatives were below the threshold values for delineation of a novel species, (ANIm ranging from 87.5 to 88.6, AAI ranging from 80.6 to 84.6, and dDDH ranging from 28.4 to 31.7), respectively. A taxonomic position of strain CH9-7(T) in the phylogenomic tree showed that the closest relative strain was S. lydicus NBRC 13058 (T). The comparative phenotypic studies between strain CH9-7(T) and its closest relatives revealed that strain CH9-7(T) could be classified as a novel species of the genus Streptomyces. Thus, the name Streptomyces siderophoricus sp. nov. is proposed for the strain. The type strain is CH9-7(T) ( = TBRC 17833 (T) = NBRC 116426 (T)). The chemical investigation led to the isolation of four known compounds (compounds 1-4). Among these compounds, compound 1 was identified to be nocardamine, a promising bioactive substance.