Characterization of the bacterial phytochrome BphP of Pseudomonas aeruginosa
The ability to sense and respond to different environmental conditions allows bacteria to adapt quickly to their surroundings. Genome analysis revealed that the opportunistic human pathogen Pseudomonas aeruginosa encodes the bacteriophytochrome PaBphP, a red/ far red light sensor. Phytochromes constitute a major photoreceptor family found in plants, algae, fungi, and bacteria. These photochromic biliproteins have been shown to play a central role in vital processes such as seed germination in plants and virulence in plant pathogens, but their function in the heterotrophic, opportunistic pathogen P. aeruginosa is still unknown.
Our work revealed that PaBphP is an in vitro- active red/ far-red light sensor histidine kinase of a two-component regulatory system. Two-component systems (TCSs) are key mediators of bacterial signal transduction, which control cellular processes such as cell division, nutrient uptake, motility, and virulence. TCSs consist of a sensor kinase that responds to specific signals by modifying the phosphorylated state of a cognate response regulator. So far, the corresponding response regulator of PaBphP has not been disclosed yet.
Our main interest is to understand the molecular mechanisms by which the light signal is perceived by PaBphP and transduced to a certain output module. By applying biochemical methods, we hope to gain insight into the downstream signaling pathway of PaBphP and advance our understanding of the role of a red/ far red light sensor in P. aeruginosa.
The Pr- enriched form ofBphP was obtained after illuminationwithfarred light (750 nm) andhas an absorptionmaximum at 700 nm. The Pfr-enriched form was obtained after illuminationwithred light (630 nm) andhas an absorptionmaximum at 750 nm. A difference spectrum specific to phytochromes was calculated from the difference between the two forms.
Signal perceptionbythesensordomainofPaBphPinducesautophosphorylationofthehistidinekinasedomain (HKD) at a conservedhistidineresidue. The phosphategroup (P) isrelayedto a conservedaspartatewithinthereceiverdomain (REC) oftheresponseregulator, which in turn regulatesthecellularresponse.