Regulation of ornibactin biosynthesis and N-acyl-L-homoserine lactone production by CepR in Burkholderia cepacia.
The CepR-CepI quorum-sensing system has been shown to regulate production of the siderophore ornibactin, extracellular proteases, and N-octanoyl-homoserine-L-lactone (OHL) in Burkholderia cepacia strain K56-2. To examine the effect of cepIR on production of other siderophores, cepR mutants were constructed in strains that produce pyochelin in addition to salicylic acid and ornibactins. Pc715j-R1 (cepR::tp) hyperproduced ornibactin but produced parental levels of pyochelin and salicylic acid, suggesting that CepR is a negative regulator of ornibactin synthesis but not pyochelin or salicylic acid. Pc715j-R1 was also protease deficient and OHL negative. The effects of cepR on ornibactin biosynthetic genes were examined by constructing cepR pvdA-lacZ and cepR pvdD-lacZ mutants and monitoring beta-galactosidase activity. There was an increase in expression of pvdA in the cepR mutant compared to the level in its parent strain in both low- and high-iron media during stationary phase. When the outer membrane protein profiles of a cepR mutant and the wild-type strain were compared on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, there did not appear to be any difference in levels of expression of the ornibactin receptor. Experiments with cepI-lacZ and cepR-lacZ transcriptional fusions indicated that cepI was not expressed in the cepR mutant and that cepR acts as a negative regulator of its own expression. By a thin-layer chromatography assay for N-acyl homoserine lactones, OHL and N-hexanoyl-L-homoserine lactone (HHL) were detectable in K56-2 and Pc715j, both wild-type strains. OHL was not detectable and HHL was only weakly detectable in the cepI and cepR mutants. These results suggest that CepR is both a positive and negative transcriptional regulator and that CepR may influence the expression of ornibactin biosynthetic genes in addition to the expression of the cepIR quorum-sensing system.
Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, Alberta, Canada T2N 4N1.
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D001426:Bacterial Proteins / Q000096:biosynthesis; D016956:Burkholderia cepacia / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006714:Homoserine / Q000031:analogs & derivatives* / Q000378:metabolism*; D007783:Lactones / Q000378:metabolism*; D008025:Ligases; D010636:Phenols / Q000378:metabolism; D018000:Receptors, Peptide / Q000502:physiology*; D020156:Salicylic Acid / Q000378:metabolism; D017262:Siderophores / Q000378:metabolism*; D013844:Thiazoles
D001426:Bacterial Proteins; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D010636:Phenols; D018000:Receptors, Peptide; D017262:Siderophores; D013844:Thiazoles; C025316:pyochelin; D006714:Homoserine; D008025:Ligases; C449816:N-acylhomoserine lactone synthase; D020156:Salicylic Acid