Comparison of the 16S-23S rRNA intergenic spacer regions among strains of the Mycoplasma mycoides cluster, and reassessment of the taxonomic positionof 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 clust er and of Mycoplasma putrefaciens suggested the presence of two subclusters . One subcluster comprised M. mycoides subsp. mycoides small colony (SC) ty pe, M. mycoides subsp. mycoides large colony (LC) type and M. mycoides subs p. capri, whereas the second subcluster comprised Mycoplasma capricolum sub sp. capricolum, M. capricolum subsp. capripneumoniae and Mycoplasma sp. bov ine group 7. The type strains from M. mycoides subsp. mycoides SC and M. my coides subsp. capri had identical spacer sequences. The existence of two su bclusters was supported by predicted secondary structures of the analysed r egion. The nucleotide variations in the loop domains of the secondary struc tures might be a useful genetic marker to distinguish between the two subcl usters. The secondary structure differences delineated the differences betw een the two subclusters more clearly than the nucleotide sequence alignment s, 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 rec lassification of Mycoplasma sp. bovine group 7 as another subspecies of M. capricolum.