Identification and characterization of the PhhR regulon in Pseudomonas putida
Article first published online: 27 DEC 2009
© 2009 Society for Applied Microbiology and Blackwell Publishing Ltd
Special Issue: Pseudomonas. Editors: Professors Burkhard Tummler, Victor de Lorenzo, Alain Filloux and Joyce Loper
Volume 12, Issue 6, pages 1427–1438, June 2010
How to Cite
Herrera, M. C., Duque, E., Rodríguez-Herva, J. J., Fernández-Escamilla, A. M. and Ramos, J. L. (2010), Identification and characterization of the PhhR regulon in Pseudomonas putida. Environmental Microbiology, 12: 1427–1438. doi: 10.1111/j.1462-2920.2009.02124.x
- Issue published online: 3 JUN 2010
- Article first published online: 27 DEC 2009
- Received 9 September, 2009; accepted 27 October, 2009.
Pseudomonas putida is a soil microorganism that utilizes aromatic amino acids present in root exudates as a nitrogen source. We have previously shown that the PhhR transcriptional regulator induces phhAB genes encoding a phenylalanine hydroxylase. In this study we show, using microarray assays and promoter fusions, that PhhR is a global regulator responsible for the activation of genes essential for phenylalanine degradation, phenylalanine homeostasis and other genes of unknown function. Recently, it has been shown that phenylalanine catabolism occurs through more than one pathway. One of these possible pathways involves the metabolism of phenylalanine via tyrosine, p-hydroxyphenylpyruvate, and homogentisate. We identified two genes within this pathway that encode an acyl-CoA transferase involved in the metabolism of acetoacetate. All genes in this pathway were induced in response to phenylalanine in a PhhR-proficient background. The second potential degradative pathway involves the degradation of phenylalanine to produce phenylpyruvate, which seems to be degraded via phenylacetyl-CoA. A number of mutants in the paa genes encoding phenylacetyl-CoA degradation enzymes fail to grow on phenylpyruvate or phenylacetate, further supporting the existence of this second pathway. We found that the PhhR regulon also includes genes involved in the biosynthesis of aromatic amino acids that are repressed in the presence of phenylalanine, suggesting the possibility of feedback at the transcriptional level. In addition, we found that PhhR modulates the level of expression of the broad-substrate-specificity MexEF/OprN efflux pump. Expression from this pump is under the control of mexT gene product because phenylalanine-dependent transcription from the mexE promoter does not occur in a mexT mutant background. These results place PhhR as an important regulator in the control of bacterial responses to aromatic amino acids.