In enterobacteria genomes, mutS and rpoS, encoding one of the main components of DNA mismatch repair and the alternative stationary-phase rpoS factor respectively, are located in a highly polymorphic region of the chromosome. The extensive polymorphism of this region is postulated to result from cycling between environments in which the functional or non-functional mutS and rpoS genes provide distinct fitness advantages. Furthermore, in E. coli alterations in this region have been correlated with a mutS produced enhanced mutation/recombination rate and implicated in the emergence of new pathogenic clones. In spite of the importance of Pseudomonas aeruginosa as a human pathogen, there is no characterization of this segment in this versatile bacterium. By PCR amplification and restriction fragment length polymorphism (RFLP) we first analyze the extent and nature of the mutS-rpoS intergenic region in sixteen different P. aeruginosa Cystic Fibrosis isolates as well as in the PAO1 and the soil isolated Hex1T strains. Interestingly, we observed that the length of that region was equivalent in all the strains analyzed, which in addition to the RFLP analysis suggest it would be unexpectedly conserved. Further studies are being carried out in order to analyze the structure of this region in P. aeruginosa and the consequences associated with mutS mutations and loss of DNA mismatch repair.
