Phylogenetic analysis reveals new relationships among members of the genera Microtetraspora and Microbispora

The 16S rRNA gene sequences of 7 Microbispora strains, 14 Microtetraspora species, 9 Streptosporangium species, and 12 Actinomadura species were determined. A phylogenetic analysis showed that Microtetraspora fusca, Microtetraspora glauca, and Microtetraspora niveoalba formed a coherent cluster with the members of the genus Microbispora. This cluster is distantly related to two other clusters, one of which consists of the Microtetraspora species transferred from the former Actinomadura pusilla group and one of which consists of members of the genus Streptosporangium. Our results show that it is necessary to review the taxonomic definitions of the genera Microtetraspora and Microbispora, which have been separated by a single morphological characteristic, the number of spores on spore chains.