Proteolytic regulation of alginate overproduction in Pseudomonas aeruginosa
F Heath Damron1, Joanna B Goldberg
1Department of Microbiology, Immunology, and Cancer Biology, University of Virginia Health System, Charlottesville, VA, USA.
Abstract:
Pseudomonas aeruginosa, a Gram-negative bacterium, is a significant opportunistic pathogen associated with skin and soft tissue infections, nosocomial pneumonia and sepsis. In addition, it can chronically colonize the lungs of cystic fibrosis (CF) patients. Overproduction of the exopolysaccharide called alginate provides P. aeruginosa with a selective advantage and facilitates survival in the CF lung. The in vitro phenotype of alginate overproduction observed on solid culture media is referred to as mucoid. Expression of the alginate machinery and biosynthetic enzymes are controlled by the extracytoplasmic sigma factor, σ(22) (AlgU/T). The key negative regulator of both σ(22) activity and the mucoid phenotype is the cognate anti-sigma factor MucA. MucA sequesters σ(22) to the inner membrane inhibiting the sigma factor's transcriptional activity. The well-studied mechanism for transition to the mucoid phenotype is mutation of mucA, leading to loss of MucA function and therefore activation of σ(22) . Recently, regulated intramembrane proteolysis (RIP) has been recognized as a mechanism whereby proteolysis of the anti-sigma factor MucA leads to active σ(22) allowing P. aeruginosa to respond to environmental stress conditions by overproduction of alginate. The goal of this review is to illuminate the pathways leading to RIP that have been identified and proposed.
Insights
Pseudomonas aeruginosa overproduces alginate, causing infections, especially in cystic fibrosis patients. Recent studies reveal regulated intramembrane proteolysis (RIP) as a key pathway activating alginate production.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen causing various infections, notably in cystic fibrosis patients.
- Alginate overproduction, termed mucoid phenotype, enhances bacterial survival, particularly in the cystic fibrosis lung.
- The sigma factor σ(22) (AlgU/T) controls alginate production, negatively regulated by the anti-sigma factor MucA.
Purpose of the Study:
- To review the mechanisms of regulated intramembrane proteolysis (RIP) of MucA.
- To elucidate how RIP leads to σ(22) activation and alginate overproduction.
- To highlight pathways identified and proposed for MucA RIP.
Main Methods:
- Literature review of studies on Pseudomonas aeruginosa, alginate production, and sigma factor regulation.
- Analysis of mechanisms involving MucA, σ(22), and regulated intramembrane proteolysis.
- Synthesis of current understanding of the transition to the mucoid phenotype.
Main Results:
- Loss-of-function mutations in mucA are a known cause of the mucoid phenotype.
- Regulated intramembrane proteolysis (RIP) of MucA is a newly recognized pathway for activating σ(22).
- RIP allows P. aeruginosa to increase alginate production in response to environmental stress.
Conclusions:
- RIP of MucA is a critical mechanism controlling alginate overproduction in P. aeruginosa.
- Understanding RIP pathways is crucial for developing strategies against P. aeruginosa infections, especially in cystic fibrosis.
- Further research into RIP mechanisms can reveal new therapeutic targets.
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