SMANIA ANDREA
Congresos y reuniones científicas
Título:
Involvement of MutS in Pseudomonas aeruginosa adaptive mutagenesis: The acquisition of quorum-sensing-deficient (lasR) phenotype as an illustrative model.
Autor/es:
LUJÁN AM; MOYANO AJ; ARGARAÑA CE; SMANIA AM
Lugar:
Buenos Aires
Reunión:
Congreso; IV Reunión Anual de la SAMIGE; 2007
Resumen:
The potential role of mutators in evolution has been an issue of major biological and medical concern. Most of the mutator bacteria isolated in nature have been shown to be defective in the Mismatch Repair System (MMR), whose deficiency generates not only a mutator but also a hyperecombinogenic phenotype. Interestingly, Pseudomonas aeruginosa mutator clones are extremely frequent in Cystic Fibrosis (CF) chronic infections, suggesting that they play a crucial role in the adaptation required for long-term establishment in the heterogeneous and changing CF lung environment. Most of these mutator strains were found to be deficient in the mutS gene, one of the main components of the MMR. Also, defects in the lasR gene, a major regulator of the P. aeruginosa Quorum Sensing (QS) system, have been detected in chronic infections suggesting that inactivation of LasR would be advantageous for P. aeruginosa persistence. We recently found that inactivation of mutS in P. aeruginosa results in the spontaneous and reproducible emergence of defined morphological colony variants after cultivation in aerated rich medium to late stationary-phase, in contrast to the non-mutator parental strain, which does not display any kind of diversification under identical incubation conditions. One of the morphotypical variants, mS2, emerges at a high frequency and displays differences in virulence traits commonly regulated by QS. The present study shows that mS2 variants had defective LasR function due to simple but different point mutations along the lasR gene sequence, indicating that LasR inactivation is the main cause of mS2 phenotypic diversification. Moreover, no sequence alterations were found in the gacA and rhlR genes, two major QS regulators, suggesting that the selective pressures for GacA/RhlR and LasR were not the same and differed from those in other Pseudomonas species, which, when incubated in nutrient-rich liquid stationary-phase cultures, show specific high instability in the gacA–gacS genes. Finally, it was determined that a non-functional LasR would confer a selective advantage in the late stationary-phase, since viability was notably higher for mS2. Our results offer evidences of the involvement of the MMR in the adaptive mutagenesis of P. aeruginosa and its relationship with stationary-phase transcriptional regulators. In this context, we are currently carrying out new investigations to determine the potential transcriptional regulation of mutS by the stationary phase sigma factor RpoS, which in Pseudomonas has been related to the QS cascade.
