The interplay of StyR and IHF regulates substrate-dependent induction and carbon catabolite repression of styrene catabolism genes in Pseudomonas fluorescens ST

• Published in: BMC microbiology Vol. 8; no. 1; p. 92
• Main Authors: Rampioni, Giordano, Leoni, Livia, Pietrangeli, Biancamaria, Zennaro, Elisabetta
• Format: Journal Article
• Language: English
• Published: London BioMed Central 11.06.2008; BioMed Central Ltd; BMC
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Base Sequence; Binding Sites; Biodegradation; Biological Microscopy; Biomedical and Life Sciences; Carbon - metabolism; Gene Expression Regulation, Bacterial; Genes, Reporter; Genetic aspects; Integration Host Factors - metabolism; Life Sciences; Microbiology; Models, Genetic; Mycology; Operon; Parasitology; Physiological aspects; Promoter Regions, Genetic; Pseudomonas fluorescens; Pseudomonas fluorescens - genetics; Pseudomonas fluorescens - metabolism; Repressor Proteins; Research Article; Styrene; Styrene - metabolism; Transcription, Genetic; Virology; Waste management; Italy; Catabolite Repression; Styrene Oxide; Styrene; Carbon Catabolite Repression; Phenylacetaldehyde
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/1471-2180-8-92

Background In Pseudomonas fluorescens ST, the promoter of the styrene catabolic operon, P styA , is induced by styrene and is subject to catabolite repression. P styA regulation relies on the StyS/StyR two-component system and on the IHF global regulator. The phosphorylated response regulator StyR (StyR-P) activates P styA in inducing conditions when it binds to the high-affinity site STY2, located about -40 bp from the transcription start point. A cis -acting element upstream of STY2, named URE, contains a low-affinity StyR-P binding site (STY1), overlapping the IHF binding site. Deletion of the URE led to a decrease of promoter activity in inducing conditions and to a partial release of catabolite repression. This study was undertaken to assess the relative role played by IHF and StyR-P on the URE, and to clarify if P styA catabolite repression could rely on the interplay of these regulators. Results StyR-P and IHF compete for binding to the URE region. P styA full activity in inducing conditions is achieved when StyR-P and IHF bind to site STY2 and to the URE, respectively. Under catabolite repression conditions, StyR-P binds the STY1 site, replacing IHF at the URE region. StyR-P bound to both STY1 and STY2 sites oligomerizes, likely promoting the formation of a DNA loop that closes the promoter in a repressed conformation. We found that StyR and IHF protein levels did not change in catabolite repression conditions, implying that P styA repression is achieved through an increase in the StyR-P/StyR ratio. Conclusion We propose a model according to which the activity of the P styA promoter is determined by conformational changes. An open conformation is operative in inducing conditions when StyR-P is bound to STY2 site and IHF to the URE. Under catabolite repression conditions StyR-P cellular levels would increase, displacing IHF from the URE and closing the promoter in a repressed conformation. The balance between the open and the closed promoter conformation would determine a fine modulation of the promoter activity. Since StyR and IHF protein levels do not vary in the different conditions, the key-factor regulating P styA catabolite repression is likely the kinase activity of the StyR-cognate sensor protein StyS.