Microbial pathogenesis in cystic fibrosis: co‐ordinate regulation of heat‐shock response and conversion to mucoidy in Pseudomonas aeruginosa

Abstract

SummaryConversion of Pseudomonas aeruginosa to the mucoid phenotype plays a major role in the pathogenesis of respiratory infections in cystic fibrosis (CF). One mechanism responsible for mucoidy is based on mutations that inactivate the anti-factor, MucA, which normally inhibits the alternative sigma factor, AlgU. The loss of MucA allows AlgU to freely direct transcription of the genes responsible for the production of the exopolysaccharide alginate resulting in mucoid colony morphology. In Escherichia coli, a close homologue of AlgU, E , directs transcription of several genes under conditions of extreme heat shock. Here we examined whether AlgU, besides its role in controlling alginate production, affects the heat-shock response in P. aeruginosa. The P. aeruginosa rpoH gene encoding a homologue of the major heat-shock sigma factor, 32 , was found to be transcribed by AlgU containing RNA polymerase from one of its promoters (P 3 ) identified in this study. Transcription of rpoH from P 3 was elevated upon exposure to extreme heat shock in an algU-dependent manner. Importantly, the AlgU-dependent promoter of rpoH was found to be activated in mucoid mucA mutants. In keeping with this observation, introduction of a wild-type mucA gene abrogated AlgU-dependent rpoH transcription in mucoid P. aeruginosa laboratory isolates and CF isolates. These results suggest that conversion to mucoidy and the heat-shock response are co-ordinately regulated in P. aeruginosa. The simultaneous activation of both systems in mucA mutants, selected in the lungs of CF patients, may have significance for the inflammatory processes characteristic of the establishment of chronic infection and ensuing clinical deterioration in CF.

The Sigma Factor AlgU (AlgT) Controls Exopolysaccharide Production and Tolerance towards Desiccation and Osmotic Stress in the Biocontrol Agent Pseudomonas fluorescens CHA0

“…This contrasts with the demonstrated involvement of AlgU in tolerance towards these stresses in P. aeruginosa (32,54,56,70) and in P. syringae (26). Activation of algU by ROIs may help these pathogens withstand the oxidative burst associated with host defense responses (19,26).…”

“…In P. aeruginosa, the algU, mucA, and mucB genes are cotranscribed and encode (respectively) the sigma factor AlgU and its main negative regulators, MucA and MucB, which act in concert to control production of the EPS alginate and the response to extreme environmental stress (19,32,50,54,57,70). In P. syringae, AlgU is also a major determinant in the regulation of alginate biosynthesis and stress response (26).…”

“…RpoS is required for tolerance of stationary-phase cultures of different Pseudomonas species towards hyperosmolarity, high temperatures, and agents generating reactive oxygen intermediates (ROIs) (23,52,61). AlgU contributes to tolerance towards osmotic, oxidative, and heat stresses in the pathogens Pseudomonas aeruginosa (32,54,56,70) and Pseudomonas syringae (26). The extracytoplasmic function sigma factor AlgU is encoded by the algU gene, which is part of a highly conserved operon in gram-negative bacteria (19,26,35,44).…”

The alternative sigma factor AlgT, but not alginate synthesis, promotes in planta multiplication of Pseudomonas syringae pv. glycinea

“…In P. aeruginosa it was shown that AlgT directs transcription of a large set of virulence determinants or toxic factors (Firoved et al, 2002;Firoved & Deretic, 2003) and of the gene encoding the main heat-shock factor RpoH (Schurr & Deretic, 1997). Microarray analysis revealed that AlgT exerts broad-range regulatory effects on approximately 6 % of the P. aeruginosa genome, with alginate and flagellar genes accounting for only one-fifth of AlgT-regulated genes (Tart et al, 2005).…”

“…The alginate biosynthetic operon in P. aeruginosa is controlled by several two-component systems and by the alternative sigma factor, AlgT (Mathee et al, 2002). AlgT of P. aeruginosa acts as a global stress response sigma factor that activates transcription of the main heat-shock sigma factor RpoH, as well as different virulence determinants or toxic factors (Firoved et al, 2002;Firoved & Deretic, 2003;Schurr & Deretic, 1997). AlgT in P. syringae (s 22 ) is encoded by the first gene of the algT-mucAB operon, which activates alginate biosynthesis by activating its own transcription and that of algD (Keith & Bender, 1999;Schenk et al, 2006).…”