Phytochromes are red/far-red light photoreceptors found in plants and have recently also been discovered in bacteria. Biochemical analysis established that the genes bphO and bphP display the two necessary phytochrome components in the opportunistic pathogen Pseudomonas aeruginosa: bphO encoding a heme oxygenase that produces the chromophore biliverdin IXα and bphP encoding the apo-phytochrome. Transcriptional analyses established that both genes form a bicistronic operon. Expression of the bphOP operon was shown to be induced in the stationary phase dependent on the alternative sigma factor, RpoS. Interestingly, the loss of BphO but not BphP led to pronounced phenotypes in the stationary phase suggesting an additional role of BphO besides providing the chromophore to BphP. Transcriptome and proteom studies on the other hand revealed that BphP is involved in the regulation of various gene clusters and pointed to a link of BphP function with the P. aeruginosa quorum sensing system