Genetic relationships among mycoplasmas based on the 16S-23S rRNA spacer sequence

The nucleotide sequences of the spacer regions between the 16S and 23S rRNA genes of 20 Mycoplasma species were determined following amplification by PCR. Although the spacer regions lacked spacer tRNA genes, they contained the box B and box A sequences in this order from the 5' terminus. The sequence alignment indicated that the 20 species were divided into four clusters, the M. pneumoniae, M. hominis, M. hyorhinis and M. fermentans clusters, and a single floating species, M. hyopneumoniae.