ANALYSIS OF THERMOPHILIC CLADES WITHIN THE GENUS STREPTOMYCES BY 16S RIBOSOMAL DNA-SEQUENCE COMPARISONS

Almost complete sequences of the 16S rRNA genes of eight representativ e thermophilic streptomycetes were determined following the isolation and cloning of the amplified genes. These sequences were aligned with those of representative mesophilic streptomycetes, and phylogenetic tr ees were inferred by using four tree-making algorithms. The thermophil ic streptomycetes formed two distinct clades that were supported by hi gh bootstrap values based on 1,000 resamplings, One clade encompassed Streptomyces macrosporus and related species, and the second clade inc luded Streptomyces thermodiastaticus and allied taxa, The relationship s between the organisms were not markedly influenced by the different tree-making methods, but the rooting of the tree was sensitive to the choice of the outgroup strain. It is evident from this study that the thermophilic streptomycetes do not merit recognition as a distinct tax on within the genus Streptomyces.