[39] Regulation of alginate gene expression in Pseudomonas aeruginosa

Alginate is an exopolysaccharide produced by Pseudomonas aeruginosa during infection of the lungs of cystic fibrosis (CF) patients. The polysaccharide is rarely produced by P. aeruginosa outside the CF lung environment (e.g., during eye, urinary tract, or burn infections), and it constitutes a major virulence factor in CF lung infections. The alginate capsule is believed not only to allow P. aeruginosa cells to adhere to the epithelial cells of the CF lung, but also to protect the infecting cells from the host immune systems and antibiotic therapy by forming a gel surrounding the cells that are found as microcolonies in the form of a biofilm on the epithelial cells. The heavily mucoid form of P. aeruginosa isolated from the CF lung is an unstable phenotype, which undergoes transition to nonmucoidy spontaneously at a rapid rate during culturing in the laboratory. This suggests that the mucoid phenotype arising from alginate production is triggered specifically in the CF lung environment. The mechanism of spontaneous switching on of the alginate biosynthetic (alg) genes in the CF lung and its switching off outside this environment is, however, little understood.