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Cell wall‐inhibitory antibiotics activate the alginate biosynthesis operon in Pseudomonas aeruginosa : roles of σ 22 (AlgT) and the AlgW and Prc proteases
Author(s) -
Wood Lynn F.,
Leech Andrew J.,
Ohman Dennis E.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05390.x
Subject(s) - biology , sigma factor , operon , repressor , pyocyanin , mutant , microbiology and biotechnology , escherichia coli , biochemistry , gene , quorum sensing , gene expression , rna polymerase , virulence
Summary 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 (P algD‐cat ), and > 50 compounds were tested for promoting chloramphenicol resistance. Most compounds showing P algD‐cat induction were cell wall‐active antibiotics that blocked peptidoglycan synthesis. P algD‐cat induction was blocked by mutations in the genes for σ 22 ( algT / algU ) or regulators AlgB and AlgR. Anti‐sigma factor MucA was the primary regulator of σ 22 activity. A transcriptome analysis using microarrays verified that the algD operon undergoes high induction by d ‐cycloserine. A similar σ 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 P algD‐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 σ 22 activation. In addition, a mutation in gene PA3257 ( prc ), encoding a Prc‐like protease, resulted in poor induction of P algD‐cat by d ‐cycloserine, suggesting that it also plays a role in the response to cell wall stress.