A soil actinomycete, strain 80-133(T), with the non-validly published name 'Microstreptospora cinerea', was the subject of a polyphasic study designed to clarify its taxonomic status. Comparative 16S rRNA gene sequence studies indicated that the organism belonged to the genus Streptomyces, a result in line with previous chemotaxonomic and morphological data. The strain belonged to the Streptomyces griseus clade, but could be distinguished from representatives of species assigned to this taxon by using DNA-DNA relatedness and phenotypic data. In light of these findings, it is proposed that the organism should be recognized as a novel species of the genus Streptomyces. The name proposed for this taxon is Streptomyces yanii sp. nov., with isolate 80-133(T) (=AS 4.1146(T)=JCM 3331(T)) as the type strain. It was also shown that representative strains of Streptomyces argenteolus, Streptomyces caviscabies, S. griseus and Streptomyces setonii belong to the same genomic species and have key phenotypic properties in common. It is proposed that S. caviscabies and S. setonii should be considered as later heterotypic synonyms of S. griseus and that S. argenteolus AS 4.1693(T) should also be assigned to this taxon.

Streptomycetes are a complex group of actinomycetes that produce diverse bioactive metabolites of commercial significance. Systematics can provide a useful framework for identifying species that may produce novel metabolites. However, previously proposed approaches to the systematics of Streptomyces have suffered from either poor interlaboratory comparability or insufficient resolution. In particular, the Streptomyces griseus 16S rRNA gene clade is the most challenging and least defined group within the genus Streptomyces in terms of phylogeny. Here we report the results of a multilocus sequence analysis scheme developed to address the phylogeny of this clade. Sequence fragments of six housekeeping genes, atpD, gyrB, recA, rpoB, trpB and 16S rRNA, were obtained for 53 reference strains that represent 45 valid species and subspecies. Analysis of each individual locus confirmed the suitability of loci and the congruence of single-gene trees for concatenation. Concatenated trees of three, four, five and all six genes were constructed, and the stability of the topology and discriminatory power of each tree were analysed. It can be concluded from the results that phylogenetic analysis based on multilocus sequences is more accurate and robust for species delineation within Streptomyces. A multilocus phylogeny of six genes proved to be optimal for elucidating the interspecies relationships within the S. griseus 16S rRNA gene clade. Our multilocus sequence analysis scheme provides a valuable tool that can be applied to other Streptomyces clades for refining the systematic framework of this genus.

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