Comparison of the 16S-23S rRNA intergenic spacer regions among strains of the Mycoplasma mycoides cluster, and reassessment of the taxonomic position of Mycoplasma sp. bovine group 7.

Nucleotide sequence analysis of the 16S-23S rRNA intergenic spacer regions of six type or reference strains belonging to the Mycoplasma mycoides cluster and of Mycoplasma putrefaciens suggested the presence of two subclusters. One subcluster comprised M. mycoides subsp. mycoides small colony (SC) type, M. mycoides subsp. mycoides large colony (LC) type and M. mycoides subsp. capri, whereas the second subcluster comprised Mycoplasma capricolum subsp. capricolum, M. capricolum subsp. capripneumoniae and Mycoplasma sp. bovine group 7. The type strains from M. mycoides subsp. mycoides SC and M. mycoides subsp. capri had identical spacer sequences. The existence of two subclusters was supported by predicted secondary structures of the analysed region. The nucleotide variations in the loop domains of the secondary structures might be a useful genetic marker to distinguish between the two subclusters. The secondary structure differences delineated the differences between the two subclusters more clearly than the nucleotide sequence alignments, which only showed a small number of differences, and some of these were common to both clusters. The data also provided evidence in favour of a reclassification of Mycoplasma sp. bovine group 7 as another subspecies of M. capricolum.