title: Cell wall-inhibitory antibiotics activate the alginate biosynthesis operon in Pseudomonas aeruginosa: Roles of sigma (AlgT) and the AlgW and Prc proteases.
abstract: A bioassay was developed to identify stimuli that promote the transcriptional induction of the algD operon for alginate biosynthesis in Pseudomonas aeruginosa. Strain PAO1 carried the algD promoter fused to a chloramphenicol acetyl-transferase cartridge (PalgD-cat), and > 50 compounds were tested for promoting chloramphenicol resistance. Most compounds showing PalgD-cat induction were cell wall-active antibiotics that blocked peptidoglycan synthesis. PalgD-cat induction was blocked by mutations in the genes for sigma22 (algT/algU) or regulators AlgB and AlgR. Anti-sigma factor MucA was the primary regulator of sigma22 activity. A transcriptome analysis using microarrays verified that the algD operon undergoes high induction by D-cycloserine. A similar sigma(E)-RseAB complex in Escherichia coli responds to envelope stress, which requires DegS protease in a regulated intramembrane proteolysis (RIP) cascade to derepress the sigma. Mutant phenotypic studies in P. aeruginosa showed that AlgW (PA4446) is likely to be the DegS functional homologue. A mutation in algW resulted in a complete lack of PalgD-cat induction by D-cycloserine. Overexpression of algW in PAO1 resulted in a mucoid phenotype and alginate production, even in the absence of cell wall stress, suggesting that AlgW protease plays a role in sigma22 activation. In addition, a mutation in gene PA3257 (prc), encoding a Prc-like protease, resulted in poor induction of PalgD-cat by D-cycloserine, suggesting that it also plays a role in the response to cell wall stress.
authors.affiliation: Department of Microbiology and Immunology, Medical College of Virginia Campus of Virginia Commonwealth University, Richmond, VA 23298-0678, USA.
authors.forename: Lynn F
authors.initials: LF
authors.lastname: Wood
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Leech
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Ohman
mesh_terms: D000464:Alginates; D000900:Anti-Bacterial Agents / Q000145:classification / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D020723:Glucuronic Acid / Q000096:biosynthesis; D006603:Hexuronic Acids; D009154:Mutation / Q000235:genetics; D009876:Operon / Q000235:genetics*; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: C097646:AlgW protein, Pseudomonas aeruginosa; D000464:Alginates; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D006603:Hexuronic Acids; D012097:Repressor Proteins; D012808:Sigma Factor; D020723:Glucuronic Acid; D010447:Peptide Hydrolases