Expression of the phytochrome operon in Pseudomonas aeruginosa is dependent on the alternative sigma factor RpoS.
Phytochromes are red/far-red light photoreceptors found in plants, cyanobacteria and heterotrophic bacteria. Biochemical analyses have established that the genes bphO and bphP (PA4116 and PA4117) of Pseudomonas aeruginosa encode both phytochrome components: BphO, a heme oxygenase that produces the linear tetrapyrrole chromophore biliverdin IXalpha, and BphP, the apo-phytochrome. Reverse transcription-PCR established that both genes form a bicistronic operon. Expression of the bphOP operon was induced in the stationary phase, indicating an involvement of the P. aeruginosa quorum-sensing system and/or the stationary-phase alternative sigma factor RpoS. Bioinformatic analyses of the promoter region revealed a potential binding site for the quorum sensing regulators LasR and/or RhlR. While a direct involvement of the quorum-sensing system could be ruled out, the dependence of bphOP expression on RpoS was clearly demonstrated. Chromosomal knock-out mutants showed identical growth behavior as a wild type under various conditions but increased levels of pyocyanin were detected in the DeltabphO strain. Additionally, this strain showed decreased heat tolerance in the stationary phase, indicating a potential protective role of the BphO reaction product biliverdin. Therefore, BphO might have an additional function besides providing the chromophore for BphP and both proteins are likely to fulfill a task in the stationary phase.
Barkovits
Katalin
K
Physiology of Microorganisms, Ruhr-University Bochum, Bochum, Germany.
Harms
Andrea
A
Benkartek
Corinna
C
Smart
James L
JL
Frankenberg-Dinkel
Nicole
N
D001664:Biliverdine / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000502:physiology; D009876:Operon; D010834:Phytochrome / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism*; D053038:Quorum Sensing / Q000235:genetics; D018085:Regulon / Q000502:physiology*; D012808:Sigma Factor / Q000502:physiology*
D012808:Sigma Factor; D010834:Phytochrome; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); D001664:Biliverdine