Contribution of the RsaL global regulator toPseudomonas aeruginosavirulence and biofilm formation

Abstract

In Pseudomonas aeruginosa, acyl-homoserine-lactone quorum sensing (acyl-HSL QS) regulates the expression of virulence factors and biofilm formation in response to cell density. The RsaL protein represses transcription of the lasI gene, encoding the 3OC(12)-HSL signal synthase. The level of 3OC(12)-HSL is 10-fold higher in an rsaL mutant than in the wild type. In this work, we studied the effect of 3OC(12)-HSL overproduction caused by the rsaL mutation by comparing the transcriptional profiles and virulence-related phenotypes of a P. aeruginosa rsaL mutant and its wild-type parent. Results showed that the rsaL mutant overproduces secreted virulence factors (pyocyanin, elastase, hemolysins), displays increased twitching and swarming motility and is hypervirulent compared with the wild type. Interestingly, the rsaL mutant is impaired in biofilm formation. Taken together, these results suggest that RsaL could be important in the transition of P. aeruginosa from a planktonic to a sessile life style and in chronic infections, characterized by biofilm formation and limited virulence factor production.

Functional Characterization of the Quorum Sensing Regulator RsaL in the Plant-Beneficial Strain Pseudomonas putida WCS358

“…The observation that the abolition of 3OC 12 -HSL production in the ppuI mutant had no significant effect on biofilm formation and pyoverdine production supports the latter hypothesis. The physiological role played by RsaL in P. putida WCS358 is similar to that observed in P. aeruginosa PAO1, since the RsaL protein of P. aeruginosa was also shown to have a positive effect on biofilm formation and to repress the production of secreted secondary metabolites (31). In contrast, the lack of an effect of the ppuI mutation on the biofilm phenotype was surprising, since previous studies with P. putida strains IsoF and PCL1445 showed that this mutation causes a significant alteration in biofilm production (3,11,35).…”

“…In all these bacteria, RsaL represses the expression of the signal synthase gene and (with the sole exception of P. fuscovaginae) causes a decrease in signal molecule production. However, the RsaL protein has been investigated at the physiological and molecular levels only in P. aeruginosa PAO1 (29)(30)(31)(32).…”

“…Accordingly, this mutant is hypervirulent in the Galleria mellonella wax moth virulence model. Moreover, the P. aeruginosa PAO1 rsaL mutant produces less biofilm and shows enhanced antibiotic susceptibility with respect to the wild type (31). These phenotypic alterations are partially due to the inability of a P. aeruginosa rsaL mutant to maintain the QS signal molecule 3OC 12 -HSL at physiologically advantageous levels (32).…”

Global Regulatory Pathways and Cross-talk ControlPseudomonas aeruginosaEnvironmental Lifestyle and Virulence Phenotype

“…Rampioni et al (2007) demonstrated that while RsaL and LasR are capable of binding simultaneously to the intergenic region; repression by RsaL supersedes LasR-mediated activation (Rampioni, 2007). RsaL appears to be a global regulator, controlling ~130 genes independent of its effect on lasI expression (Rampioni, 2007), including genes whose products are involved in antibiotic resistance and biofilm formation in P. aeruginosa (Rampioni, 2009). Evidence for rsaL upregulation was found in P. aeruginosa RNA harvested from sputum samples obtained from chronically infected CF patients, suggesting that RsaL plays a role in C12-HSL homeostatic control during chronic infection (Son, 2007).…”

Pseudomonas Aeruginosa AmpR Transcriptional Regulatory Network

“…RsaL also appears to be important in regulating the transition from planktonic to a sessile state as rsaL mutants exhibit increased swarming motility and fail to form biofilms (636).…”