Pulmonary infection by mucoid, alginate-producing Pseudomonas aeruginosa is the leading cause of mortality among patients suffering from cystic fibrosis. Alginate-producing P. aeruginosa is uniquely associated with the environment of the cystic fibrosis-affected lung, where alginate is believed to increase resistance to both the host immune system and antibiotic therapy. Recent evidence indicates that P. aeruginosa is most resistant to antibiotics when the infecting cells are present as a biofilm, as they appear to be in the lungs of cystic fibrosis patients. Inhibition of the protective alginate barrier with nontoxic compounds targeted against alginate biosynthetic and regulatory proteins may prove useful in eradicating P. aeruginosa from this environment. Our research has dealt with elucidating the biosynthetic pathway and regulatory mechanism(s) responsible for alginate synthesis by P. aeruginosa. This review summarizes reports on the role of alginate in cystic fibrosis-associated pulmonary infections caused by P. aeruginosa and provides details about the biosynthesis and regulation of this exopolysaccharide.

The exopolysaccharide alginate is a maJor virulence factor ofPseudomonas aeruginosa strains that infect the lungs of cystic fibrosis patients. The synthesis of alginate is almost uniquely associated with the pathogenicity ofP. aeruginosa within the environment of the cystic fibrosis lung. The gene a4gC is one of the essential alginate biosynthetic genes and codes for the enzyme phosphomannomutase. In this report, we present data on the transcriptional regulation of algC expression. The activity of the algC promoter is modulated by the response regulator, AlgR1, a member of the two-component signal transduction protein family, which also regulates other alginate-specific promoters. In both mucoid (alginate-positive) and nonmucoid (alginate-negative) P. aeruginosa strains, transcriptional activation ofalgC increased with the osmolarity of the culture medium. This osmolarity-induced activation was found to be dependent on AlgRl. AlgRl was found to interact directly with the algC promoter. Deletion mapping, in conjunction with mobility shift assays, showed that AlgRl specifically bound with two regions ofalgC upstream DNA. A fragment spanning nucleotide positions -378 to -73 showed strong specific binding, while a fragment located between positions -73 and +187 interacted relatively weakly with AlgR1. Phosphorylation of the AlgRl protein resulted in the stimulation of its in vitro ability to bind to the algC promoter region (a fragment spanning nucleotides -378 to -73). Transcription from the aIgC promoter, which has significant homology with the RNA polymerase o-54 (RpoN) recognition sequence, decreased in an rpoN mutant of P. aeruginosa.

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