Abstract
ABSTRACTCystic fibrosis (CF) is a genetic disorder that leads to a buildup of mucus in the lungs ideal for bacterial colonization. WhenPseudomonas aeruginosaenters the CF lung, it undergoes a conversion from nonmucoid to mucoid; colonization by a mucoid strain ofP. aeruginosagreatly increases mortality. The mucoid phenotype is due to the production of alginate. The regulator of alginate production is the AlgT/U sigma factor. The observed phenotypic conversion is due to a mutation in themucAgene coding for an anti-sigma factor, MucA, which sequesters AlgT/U. This mucoid phenotype is unstable when the strains are removed from the lung as they acquire second-site mutations. Thisin vitroreversion phenomenon is utilized to identify novel genes regulating alginate production. Previously, second-site mutations were mapped toalgT/U, algO,andmucP, demonstrating their role in alginate regulation. Most of these studies were performed using a non-CF isolate. It was hypothesized that second site mutations in a clinical strain would be mapped to the same genes. In this study, a clinical, hyper-mucoidP. aeruginosastrain PA2192 was used to study the reversion phenomenon. This study found that PA2192 has a novelmucAmutation which was named themmucA180allele. Twelve colonies were sub-cultured for two weeks without aeration at room temperature in order to obtain nonmucoidsuppressors ofalginateproduction(sap). Only 41sapmutants were stable for more than 48 hours — a reversion frequency of 3.9% as compared to ~90% in laboratory strains showing that PA2192 has a stable mucoid phenotype. This phenotype was restored in 28 of the 41sapmutants when complemented with plasmids harboringalgT/U. Four of thesapmutants are complemented byalgO. Sequence analyses of thealgT/Umutants have found no mutations in the coding region or promoter leading to the hypothesis that there is another, as yet unidentified mechanism of alginate regulation in this clinical strain.
Publisher
Cold Spring Harbor Laboratory
Cited by
3 articles.
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