Genomic diversity in 21 strains of and 10 strains of was investigated by random amplified polymorphic DNA (RAPD) analysis, which samples the whole genome, and by two PCR fingerprinting techniques sampling the hypervariable spacers between the conserved 16S and 23S rRNA genes of the rRNA gene operon (ITS-PCR) and regions between tRNA genes (tDNA-PCR). RAPD analysis showed a remarkable diversity among strains of that was not observed with the rRNA and tRNA intergenic-spacer-targeted PCR, where all the strains showed practically identical fingerprints. A wide variability among the strains was also observed in the plasmid profiles, suggesting that the genetic diversity within species can arise from plasmid transfer. One contribution to the diversity detected by RAPD analysis was determined by the presence of large extrachromosomal elements that were amplified during RAPD analysis as shown by Southern hybridization experiments. In contrast to the strains of , the 10 strains of were grouped into two clusters which were the same with all the methods employed. The 16S rRNA genes were identical in all 10 strains when examined using single strand conformation polymorphism analysis after digestion with and . From these data we hypothesize two different evolutionary schemes for the two species.


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