Overproduction of the AlgT Sigma Factor Is Lethal to Mucoid Pseudomonas aeruginosa
Ashley R Cross1,2, Vishnu Raghuram1,2, Zihuan Wang1,2
1Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia, USA.
Abstract:
Pseudomonas aeruginosa isolates from chronic lung infections often overproduce alginate, giving rise to the mucoid phenotype. Isolation of mucoid strains from chronic lung infections correlates with a poor patient outcome. The most common mutation that causes the mucoid phenotype is called mucA22 and results in a truncated form of the anti-sigma factor MucA that is continuously subjected to proteolysis. When a functional MucA is absent, the cognate sigma factor, AlgT, is no longer sequestered and continuously transcribes the alginate biosynthesis operon, leading to alginate overproduction. In this work, we report that in the absence of wild-type MucA, providing exogenous AlgT is toxic. This is intriguing, since mucoid strains endogenously possess high levels of AlgT. Furthermore, we show that suppressors of toxic AlgT production have mutations in mucP, a protease involved in MucA degradation, and provide the first atomistic model of MucP. Based on our findings, we speculate that mutations in mucP stabilize the truncated form of MucA22, rendering it functional and therefore able to reduce toxicity by properly sequestering AlgT.IMPORTANCEPseudomonas aeruginosa is an opportunistic bacterial pathogen capable of causing chronic lung infections. Phenotypes important for the long-term persistence and adaption to this unique lung ecosystem are largely regulated by the AlgT sigma factor. Chronic infection isolates often contain mutations in the anti-sigma factor mucA, resulting in uncontrolled AlgT and continuous production of alginate in addition to the expression of ∼300 additional genes. Here, we report that in the absence of wild-type MucA, AlgT overproduction is lethal and that suppressors of toxic AlgT production have mutations in the MucA protease, MucP. Since AlgT contributes to the establishment of chronic infections, understanding how AlgT is regulated will provide vital information on how P. aeruginosa is capable of causing long-term infections.
Insights
Pseudomonas aeruginosa mucoid strains overproduce alginate due to mucA mutations. Suppressors of toxic AlgT levels in these infections reveal mutations in MucP protease, stabilizing MucA and regulating alginate production.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Pseudomonas aeruginosa chronic lung infections often exhibit a mucoid phenotype, linked to poor patient outcomes.
- This mucoid phenotype typically results from mucA mutations, leading to uncontrolled AlgT activity and alginate overproduction.
- Alginate production and other virulence factors are regulated by the AlgT sigma factor, crucial for bacterial adaptation in chronic infections.
Purpose of the Study:
- To investigate the toxicity of exogenous AlgT in Pseudomonas aeruginosa lacking wild-type MucA.
- To identify genetic suppressors of toxic AlgT production.
- To elucidate the role of MucP protease in regulating AlgT activity and the mucoid phenotype.
Main Methods:
- Analysis of Pseudomonas aeruginosa isolates from chronic lung infections.
- Genetic screening for suppressors of toxic AlgT.
- Development of the first atomistic model of the MucP protease.
- Proteolysis assays and AlgT sequestration studies.
Main Results:
- Exogenous AlgT is toxic in Pseudomonas aeruginosa strains lacking wild-type MucA.
- Mutations in mucP, encoding a MucA-degrading protease, suppress toxic AlgT levels.
- The atomistic model of MucP provides insights into its protease function.
- MucP mutations appear to stabilize a functional truncated MucA (MucA22), reducing AlgT toxicity.
Conclusions:
- MucP plays a critical role in regulating AlgT activity by controlling MucA stability.
- Stabilization of MucA, even in truncated forms, can mitigate the toxicity associated with AlgT overproduction.
- Understanding MucP-mediated regulation offers potential therapeutic targets for Pseudomonas aeruginosa chronic infections.
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