The global posttranscriptional regulator RsmA modulates production of virulence determinants and N-acylhomoserine lactones in Pseudomonas aeruginosa

Posttranscriptional control is known to contribute to the regulation of sec ondary metabolism and virulence determinants in certain gram-negative bacte ria. Here we report the isolation of a Pseudomonas aeruginosa gene which en codes a global translational regulatory protein, RsmA (regulator of seconda ry metabolites). Overexpression of rsmA resulted in a substantial reduction in the levels of extracellular products, including protease, elastase, and staphylolytic (LasA protease) activity as well as the PA-IL lectin, hydrog en cyanide (HCN), and the phenazine pigment pyocyanin. While inactivation o f rsmA in P. aeruginosa had only minor effects on the extracellular enzymes and the PA-IL lectin, the production of HCN and pyocyanin was enhanced dur ing the exponential phase. The influence of RsmA on N-acylhomoserine lacton e-mediated quorum sensing was determined by assaying the levels of N-(3-oxo dodecanoyl)homoserine lactone (3-oxo-C12-HSL) and N-butanoylhomoserine lact one (C4-HSL) produced by the rsmA mutant and the rsmA-overexpressing strain . RsmA exerted a negative effect on the synthesis of both 3-oxo-C12-HSL and C4-HSL, which was confirmed by using lasI and rhlI translational fusions. These data also highlighted the temporal expression control of the lasI gen e, which was induced much earlier and to a higher level during the exponent ial growth phase in an rsmA mutant. To investigate whether RsmA modulates H CN production solely via quorum-sensing control, hen translational fusions were employed to monitor the regulation of the cyanide biosynthesis genes ( hcnABC). RsmA was shown to exert an additional negative effect on cyanogene sis posttranscriptionally by acting on a region surrounding the hcnA riboso me-binding site. This suggests that, in P. aeruginosa, RsmA functions as a pleiotropic posttranscriptional regulator of secondary metabolites directly and also indirectly by modulating the quorum-sensing circuitry.