Pyocyanin

Pyocyanin is a blue secondary metabolite produced by the bacterium Pseudomonas aeruginosa. It is a redox-active phenazine pigment that contributes to the characteristic coloration of P. aeruginosa colonies and can be detected in culture filtrates and clinical samples such as sputum.

Biosynthesis and regulation occur via the phenazine biosynthetic gene cluster phzA-G, which produces phenazine-1-carboxylic acid (PCA) as a precursor. Enzymes such as PhzM and PhzS convert PCA to pyocyanin through methylation and oxidation steps. Production is influenced by regulatory networks including quorum sensing (LasR and RhlR) and by environmental factors such as iron availability and oxygen levels.

Mechanistically, pyocyanin is involved in redox cycling and generates reactive oxygen species, including superoxide and hydrogen peroxide. This activity can damage host tissues, impair immune cell function, and interfere with ciliary beating and epithelial integrity. As a virulence factor, pyocyanin promotes persistence of P. aeruginosa during infections, particularly in the respiratory tracts of individuals with cystic fibrosis, though it may also be produced in wounds and other sites.

Clinical and laboratory aspects include its use as a marker of P. aeruginosa activity in research and, in some contexts, clinical microbiology. Quantification typically involves solvent extraction (often with chloroform) followed by acidification, with spectrophotometric measurement around 520 nm. Pyocyanin also serves as a tool in studies of redox biology and pathogenesis.