MOLECULAR EVOLUTION OF MYCOPLASMA-CAPRICOLUM SUBSP CAPRIPNEUMONIAE STRAINS, BASED ON POLYMORPHISMS IN THE 16S RIBOSOMAL-RNA GENES

Mycoplasma capricolum subsp. capripneumoniae belongs to the so called Mycoplasma mycoides cluster and is the causal agent of contagious capr ine pleuropneumonia (CCPP), All members of the M. mycoides cluster hav e two rRNA operons. The sequences of the 16S rRNA genes of both rRNA o perons from 20 strains of ill capricolum subsp, capripneumoniae of dif ferent geographical origins in Africa and Asia were determined. Nucleo tide differences which were present in only one of the two operons (po lymorphisms) were detected in 24 positions. The polymorphisms were not randomly distributed in the 16S rRNA genes, and some of them were fou nd in regions of low evolutionary variability. Interestingly, 11 polym orphisms were found in all the nl. capricolum subsp, capripneumoniae s trains, thus defining a putative ancestor. A sequence length differenc e between the 16S rRNA genes in a poly(A) region and 12 additional pol ymorphisms were found in only one or some of the strains. A phylogenet ic tree was constructed by comparative analysis of the polymorphisms, and this tree revealed two distinct lines of descent. The nucleotide s ubstitution rate of strains within line II was up to 50% higher than w ithin line I. A tree was also constructed from individual operonal 16S rRNA sequences, and the sequences of the two operons were found to fo rm two distinct clades. The topologies of both clades were strikingly similar, which supports the use of 16S rRNA sequence data from homolog ous operons for phylogenetic studies. The strain-specific polymorphism patterns of the 16S rRNA genes of M. capricolum subsp. capripneumonia e may be used as epidemiological markers for CCPP.