AbstractPartial nucleotide sequences (120 bp) of the 16S rRNA gene (rDNA) containing V22 variable region were compared in 357 strains of Streptomyces . Most of the Streptomyces strains fell into one large cluster-group. By sharing the same 16S rDNA sequences or very high similarity , they were clustered into five major , three middle and eight minor clusters , and 19 strains recovered as single member clusters. The result demonst rated that the phenotypic clusters , which contains st rains that are different in terms of morphologic characteristics , such as spore color and spore surface , is very heterogeneous from a molecular systematic stand point .