Sequence analysis of domain III and IV of the 23S rRNA gene of verticillate actinomycetes.

Domains III and IV of the 23S rRNA gene of 25 strains of verticillate streptomycetes were sequenced. None of the sequences was identical to any other, with regions of variability being restricted to parts of helices 54 and 64. No relationships were detected between the similarities in the sequence and the assignment to phenetic clusters as defined by the numerical taxonomy studies. Limited agreement was also found between similarity of the sequences and DNA-DNA homology values. However, species (S 70% DNA-DNA homology values)-specific diagnostic oligonucleotides generally could be defined, except for Streptomyces baldaccii. Therefore the determination of the 23S rRNA sequence may be of greater value for fingerprinting individual strains than for taxonomic or identification purposes.