RsaL, a novel repressor of virulence gene expression in Pseudomonas aeruginosa

As components of a Pseudomonas aeruginosa quorum-sensing system, LasR and P AT-I globally regulate expression of multiple virulence determinants, as we ll as the second P. aeruginosa quorum-sensing system. To date, no informati on exists on negative regulation of the quorum-sensing cascade in P. aerugi nosa. Here we describe a novel gene, rsaL, which is located downstream from lasR and transcribed antisense relative to lasR. In P. aeruginosa, overexp ression of rsaL results in reduced lasB expression and decreased elastase a ctivity. With the use of a six-His protein fusion system, we demonstrate th at rsaL encodes an 11-kDa protein. Direct quantitation of PAI-1 levels in c ultures and studies utilizing Escherichia coli lambda lysogens carrying lac Z transcriptional fusions reveal that RsaL specifically represses transcrip tion of the PAI-1 autoinducer synthase gene, lasI RsaL's repressive effect on lasI and the associated decrease in elastase activity have important imp lications for the expression of all LasR-PAI-1-dependent virulence genes an d the overall pathogenicity of P. aeruginosa.