Pseudomonads

The adaptation of the opportunistic human pathogen Pseudomonas aeruginosa often produces phenotypic diversity. Here, mutants isolated from a genetic screen show notable differences in phenotype: the production of pigments, size, shape, and texture. The blue-green pigmentation seen in some mutants results from the production of pyocyanin, an excreted toxin that kills other microbes and mammalian cells. Whereas, the brown pigmentation is caused by the exocellular pigment, pyomelanin, which is thought to protect Pseudomonas from oxidative stress.