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Journal of Bacteriology, June 2004, p. 3439-3446, Vol. 186, No. 11
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.11.3439-3446.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The davDT Operon of Pseudomonas putida, Involved in Lysine Catabolism, Is Induced in Response to the Pathway Intermediate -Aminovaleric Acid

Department of Biochemistry and Molecular and Cell Biology of Plants, Estación Experimental del Zaidín, CSIC, E-18008 Granada, Spain,¹ Molecular Microbial Ecology Group, BioCentrum DTU, 2800 Lyngby, Denmark²

Received 2 December 2003/ Accepted 17 February 2004

Pseudomonas putida KT2440 is a soil microorganism that attaches to seeds and efficiently colonizes the plant's rhizosphere. Lysine is one of the major compounds in root exudates, and P. putida KT2440 uses this amino acid as a source of carbon, nitrogen, and energy. Lysine is channeled to -aminovaleric acid and then further degraded to glutaric acid via the action of the davDT gene products. We show that the davDT genes form an operon transcribed from a single ⁷⁰-dependent promoter. The relatively high level of basal expression from the davD promoter increased about fourfold in response to the addition of exogenous lysine to the culture medium. However, the true inducer of this operon seems to be -aminovaleric acid because in a mutant unable to metabolize lysine to -aminovaleric acid, this compound, but not lysine, acted as an effector. Effective induction of the P. putida P_davD promoter by exogenously added lysine requires efficient uptake of this amino acid, which seems to proceed by at least two uptake systems for basic amino acids that belong to the superfamily of ABC transporters. Mutants in these ABC uptake systems retained basal expression from the davD promoter but exhibited lower induction levels in response to exogenous lysine than the wild-type strain.

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