Nitrosative stress inhibits production of the virulence factor alginate in mucoid Pseudomonas aeruginosa.

Alginate is a critical virulence factor contributing to the poor clinical prognosis associated with the conversion of Pseudomonas aeruginosa to mucoid phenotypes in cystic fibrosis (CF). An important mechanism of action is its ability to scavenge host innate-immune reactive species. We have previously analyzed the bacterial response to nitrosative stress by S-nitrosoglutathione (GSNO), a physiological NO radical donor with diminished levels in the CF lung. GSNO substantially increased bacterial nitrosative and oxidative defenses and so we hypothesized a similar increase in alginate production would occur. However, in mucoid P. aeruginosa, there was decreased expression of the majority of alginate synthetic genes. This microarray data was confirmed both by RT-PCR and at the functional level by direct measurements of alginate production. Our data suggest that the lowered levels of innate-immune nitrosative mediators (such as GSNO) in the CF lung exacerbate the effects of mucoid P. aeruginosa, by failing to suppress alginate biosynthesis.