H-056. A New Player in the Pseudomonas aeruginosa Quorum Sensing Circuitry

R. L. Baldini1, A. P. B. Nascimento1, V. Dekimpe2, E. Déziel2, L. G. Rahme3;
1Univ. de São Paulo, São Paulo, BRAZIL, 2INRS-Institut Armand-Frappier, Laval, QC, CANADA, 3Harvard Med. Sch., Boston, MA.

Pseudomonas aeruginosa is an ubiquitous bacterium that may act as an opportunistic pathogen. It is a major cause of morbidity and mortality in immunocompromised individuals, burn victims and people suffering from cystic fibrosis. A PA14 isogenic mutant, D12, has been previously described as less virulent in the Drosophila model host (Apidianakis et al., PNAS 102: 2573 2005). This mutant has a deletion in a gene predicted to encode a putative methyltransferase of unknown function. Besides the attenuated-in-virulence phenotype, D12 produces more pyocyanin due to higher expression levels of the phz1 operon, as assessed using a lacZ reporter fusion. It also exhibits a retarded swarming phenotype, which correlates to a delayed expression of the rhamnolipid synthesis operon rhlAB. Since the synthesis of pyocyanin and rhamnolipids is under quorum sensing control, the levels of autoinducers in D12 and PA14 cultures´ supernatants were measured using LC/MS. Whereas N-4-butanoyl-homoserine lactone (C4-HSL) and the Pseudomonas quinolone signal (PQS) levels obtained from D12 are similar to the wild-type strain, 3-oxo-dodecanoyl-HSL (oxo-C12-HSL) levels are two-fold higher in D12 supernatants. Accordingly, using reporter fusions, we found a higher level of lasI expression in D12, in agreement with the higher levels of the oxo-C12-HSL, which is synthesized by LasI. Surprinsingly, expression levels of genes required for the synthesis of C4-HSL and PQS such as rhlI and mvfR were lower in D12 than in PA14. Finally, we also found differences in the levels of the small RNA RsmZ and in rsmA expression when comparing the two strains. Although the sequence of the gene deleted in strain D12 does not present any evidence of regulatory functions, this set of data points to its involvement in the P. aeruginosa quorum sensing circuitry and its precise function is currently under investigation.