IDENTIFICATION OF THE ALGZ GENE UPSTREAM OF THE RESPONSE REGULATOR ALGR AND ITS PARTICIPATION IN CONTROL OF ALGINATE PRODUCTION IN PSEUDOMONAS-AERUGINOSA

Alginate production in mucoid Pseudomonas aeruginosa isolates from cys tic fibrosis patients is under direct control by AlgU, the P, aerugino sa equivalent of the extreme heat shock sigma factor sigma(E) in gram- negative bacteria, and AlgR, a response regulator from the superfamily of two-component signal transduction systems, In this report, we desc ribe the identification of the algZ gene, located immediately upstream of algR, which is involved in the control of alginate production, The predicted product of the algZ gene showed similarity to a subset of s ensory components from the superfamily of signal transduction systems but lacked several of the highly conserved motifs typical of histidine protein kinases, Inactivation of algZ in the wild-type standard genet ic strain PAO1 did not affect its nonmucoid morphology, However, inact ivation of algZ in a mucoid mutant P. aeruginosa strain, which had Alg U freed from control by the anti-sigma factor MucA, resulted in increa sed alginate production under growth conditions which did not permit e xpression of mucoidy in the parental algZ(+) strain, The observed effe cts were abrogated when algR was inactivated in the algZ::Tc-r backgro und, These findings indicate that algZ plays a regulatory role in algi nate production, possibly interacting with AlgR, and that it may have negative effects on expression of the mucoid phenotype under the condi tions tested, The presented results suggest that elements of negative regulation exist at the levels of both the alternative sigma factor Al gU and the transcriptional activator AlgR which, once relieved from th at suppression, cooperate to bring about the expression of the alginat e system.