DNA-DNA hybridization in the systematics of Streptomyces.

The DNA relatedness among strains in several different phenotypically defined Streptomyces species clusters was evaluated. It was found that the data from DNA-relatedness studies do not necessarily agree with the clustering generated using numerical taxonomic techniques. A study of the morphologically heterogeneous 'S. cyaneus' cluster showed that morphological criteria traditionally used to classify and identify Streptomyces species still have value, since strains in DNA-relatedness cluster groups were also similar morphologically (i.e., they had similar spore color, surface properties, and sporophore morphology). An evaluation of DNA relatedness among strains in the S. violaceusniger and S. lavendulae clusters indicated that, if anything, the genus is underspeciated, based on the number of single-member clusters observed. A study of strains of the sweet potato pathogen, S. ipomoea, collected in various locations in the United States and Japan indicated, not surprisingly, that all of the strains belong to the same species.