1887

Abstract

Mucoid strains of that overproduce the exopolysaccharide alginate are a frequent cause of chronic respiratory infections in cystic fibrosis (CF) patients. The overproduction of alginate by these strains is often caused by mutations within of the gene cluster. This gene cluster encodes an extreme stress response system composed of the ECF alternative sigma factor AlgU, the anti-sigma factor MucA located in the inner membrane and the negative regulator MucB located in the periplasm. Most of the mutations in found in mucoid strains cause a truncation of the C-terminal, periplasmic domain of MucA. The most significant effect of these mutations appears to be to reduce the levels of MucA. PA3257 () was identified as a regulator of alginate production in through the isolation and study of mutations that partially suppressed the mucoid phenotype of a strain. The uppressor f ucoidy () mutants isolated produced very little alginate when grown on LB medium, but were still mucoid when grown on Pseudomonas isolation agar. These mutations and another previously isolated suppressor mutation were complemented by cosmids or plasmids carrying PA3257. PA3257 is predicted to encode a periplasmic protease similar to Prc or Tsp of . Sequencing of from three strains with suppressor mutations confirmed that each had a mutation within the coding region. The authors propose that Prc acts to degrade mutant forms of MucA. Additional evidence in support of this hypothesis is: (1) transcription from the AlgU-regulated reporter was reduced in mutants; (2) inactivation of affected alginate production in mucoid strains with other mutations found in CF isolates; (3) inactivation or overexpression of did not affect alginate production in strains with wild-type MucA.

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2005-07-01
2019-10-23
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