The Pseudomonas aeruginosa lectins PA-IL and PA-IIL are controlled by quorum sensing and by RpoS

In Pseudomonas aeruginosa, many exoproduct virulence determinants are regul ated via a hierarchical quorum-sensing cascade involving the transcriptiona l regulators LasR and RhlR and their cognate activators, N-(3-oxododecanoyl )-L-homoserine lactone (30-C12-HSL) and N-butanoyl-L-homoserine lactone (C4 -HSL). In this paper, we demonstrate that the cytotoxic lectins PA-IL and P A-IIL are regulated via quorum sensing. Using immunoblot analysis, the prod uction of both lectins was found to be directly dependent on the rhl locus while, in a lasR mutant, the onset of lectin synthesis was delayed but not abolished. The PA-IL structural gene, lecA, was cloned and sequenced. Trans cript analysis indicated a monocistronic organization with a transcriptiona l start site 70 bp upstream of the lecA translational start codon. A lux bo x-type element together with RpoS (sigma (S)) consensus sequences was ident ified upstream of the putative promoter region. In Escherichia coli, expres sion of a lecA::lux reporter fusion was activated by RhlR/C4-HSL, but not b y LasR/3O-C12-HSL, confirming direct regulation by RhlR/C4-HSL. Similarly, in P. aeruginosa PAO1, the expression of a chromosomal lecA::lux fusion was enhanced but not advanced by the addition of exogenous C4-HSL but not 30-C 12-HSL. Furthermore, mutation of rpoS abolished lectin synthesis in P. aeru ginosa, demonstrating that both RpoS and RhlR/C4-HSL are required. Although the C4-HSL-dependent expression of the lecA::lux reporter in E. coli could be inhibited by the presence of 30-C12-HSL, this did not occur in P. aerug inosa. This suggests that, in the homologous genetic background, 30-C12-HSL does not function as a posttranslational regulator of the RhlR/C4-HSL-depe ndent activation of lecA expression.