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United States Department of Agriculture

Agricultural Research Service

Title: Benr, a Xy1s Homologue, Regulates Three Different Pathways of Aromatic Acid Degradation in Pseudomonas Putida

Authors
item Cowles, Charles - UNIV IOWA
item Nichols, Nancy
item Harwood, Caroline - UNIV IOWA

Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 29, 2000
Publication Date: N/A

Interpretive Summary: Pseudomonas putida is a soil bacterium that has been studied because it can be used to clean up pollution in soil and water and to supply basic information about metabolism. P. putida grows on some environmental pollutants, as well as many different naturally occurring compounds. The bacteria break down each of these structurally complex compounds into simple molecules. The simple molecules are then degraded through central metabolic pathways, providing carbon and energy for growth. We identified a gene, benR, that regulates three important pathways. By regulating the activity of its metabolic pathways, P. putida can carefully control the order in which it degrades a variety of compounds, allowing more efficient use of available food sources. This work contributes to our understanding of how bacteria react when they are presented with a choice of several food sources. Bacteria metabolize both naturally occurring and man-made compounds, and these results advance our understanding of how this process occurs.

Technical Abstract: Pseudomonas putida converts benzoate to catechol using two enzymes encoded on the chromosome whose expression is induced by benzoate. Benzoate binds the regulator XylS to induce expression of the TOL plasmid-encoded meta pathway operon for benzoate and methylbenzoate degradation. Benzoate also represses transport of 4-hydroxybenzoate (4-HBA) by preventing transcription of pcaK, the 4-HBA permease gene. We identified benR, a regulator of benzoate, methylbenzoate, and 4-HBA degradation genes. A benR mutant did not grow on benzoate. The deduced amino acid sequence of BenR was 62% identical to XylS, a member of the AraC family of regulators. An additional seven genes adjacent to benR were inferred from their deduced amino acid sequences to be involved in benzoate degradation. The benABC genes may encode benzoate dioxygenase, and benD may encode 2-hydro-1,2-dihydroxybenzoate dehydrogenase. benK and benF were assigned functions as a benzoate permease and porin, respectively. The function of benE is unknown. benR activated expression of a benA-lacZ reporter fusion in response to benzoate. It also activated expression of a meta cleavage operon promoter-lacZ fusion inserted in an E. coli chromosome. Third, benR was required for benzoate-mediated repression of peak expression. The benA promoter region contains a direct repeat sequence that matches the XylS binding site for the meta cleavage operon promoter. It is likely that BenR binds to the promoter region of chromosomal benzoate degradation genes and plasmid-encoded methylbenzoate degradation genes to activate gene expression in response to benzoate. The action of BenR in repressing 4-HBA uptake may be indirect.

Last Modified: 12/20/2014
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