Cystic fibrosis (CF) is a genetic disorder that leads to a buildup of mucus in the lungs ideal for bacterial colonization. When Pseudomonas aeruginosa enters the CF lung, it undergoes a conversion from nonmucoid to mucoid; colonization by a mucoid strain of P. aeruginosa greatly increases mortality. The mucoid phenotype is due to the production of alginate. The regulator of alginate production is the AlgT/U sigma factor which directs RNA polymerase to transcribe the alg regulon, thereby initiating alginate biosynthesis. The observed phenotypic conversion is due to a mutation in the mucA gene 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. This in vitro reversion phenomenon is utilized to identify novel genes regulating alginate production. Previously, second-site mutations were mapped to algT/U, algO, and mucP, 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-mucoid P. aeruginosa strain PA2192 was used to study the reversion phenomenon. This study found that PA2192 has a novel mucA mutation which was named them mucA180 allele. Twelve colonies were sub-cultured for two weeks without aeration at room temperature and plated daily for single colonies in order to obtain nonmucoid suppressors of alginate production (sap). Only 41 sap mutants 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 41 sap mutants when complimented with plasmids harboring algT/U. Four of the sap mutants are complemented by algO. Sequence analyses of the algT/U mutants have found a novel mutation in the promoter region.
