Copyright © 1994, American Society for Microbiology Analysis of Promoters Controlled by the Putative Sigma Factor AlgU Regulating Conversion to Mucoidy in Pseudomonas aeruginosa: Relationship to 0.E and Stress Response

Alginate overproduction by mucoid Pseudomonas aeruginosa is a critical pathogenic determinant expressed by this organism during chronic infections in cystic fibrosis. Conversion to mucoidy and a subsequent loss of mucoid character can occur via different mutations in the algU mucA mucB gene cluster. The algU gene encodes a 22.2-kDa putative alternative sigma factor required for expression of the critical alginate biosynthetic gene algD. In this work, algU transcription was studied by S1 nuclease protection analysis. Transcription from the promoter proximal to the algU coding region was found to be dependent on AlgU. The-35 and-10 sequences of this newly mapped promoter showed strong similarity to the promoters of two other critical aig genes: algD and algR. The proximal promoter ofalgR was also shown to depend on algU. Interestingly, the putative-35 and-10 regions of all three promoters displayed striking similarity to the consensus sequence of the UE-dependent promoters in Escherichia coli and Salmonella typhimurium. This 24-kDa cr factor, controlling genes participating in resistance to high temperatures and oxidative stress, has been previously biochemically characterized, but the gene for cE remalned unidentified. To examine whether AlgU is related to (E, the effect ofalgU inactivation on the sensitivity ofP. aeruginosa to killing by heat and reactive oxygen intermediates was tested. Two isogenic pairs of algU+ and algU mutant strains were compared. The algU mutants, irrespective of the mucoid status of the parental strains, displayed increased sensitivity to killing by paraquat, known to generate intracellular superoxide radicals, and heat. Further global homology searches revealed the presence of a previousl