Regulation of Ornibactin Biosynthesis andN-Acyl-l-Homoserine Lactone Production by CepR in Burkholderia cepacia
ABSTRACT The CepR-CepI quorum-sensing system has been shown to regulate production of the siderophore ornibactin, extracellular proteases, andN-octanoyl-homoserine-l-lactone (OHL) inBurkholderia cepacia strain K56-2. To examine the effect ofcepIR on production of other siderophores, cepRmutants 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 β-galactosidase activity. There was an increase in expression of pvdA in thecepR 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 withcepI-lacZ and cepR-lacZ transcriptional fusions indicated that cepI was not expressed in thecepR 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 andN-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 cepIand 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.