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Applied and Environmental Microbiology, August 2001, p. 3530-3541, Vol. 67, No. 8
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.8.3530-3541.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Identification and Functional Characterization of CbaR, a MarR-Like Modulator of the cbaABC-Encoded Chlorobenzoate Catabolism Pathway

Miguel A. Providenti1,2 and R. Campbell Wyndham1,*

Institute of Biology, Carleton University, Ottawa, Ontario, Canada K1S 5B6,1 and Faculty of Biology, The University, D-78457, Konstanz, Germany2

Received 23 October 2000/Accepted 15 May 2001

In Comamonas testosteroni BR60 (formerly Alcaligenes sp. strain BR60), catabolism of the pollutant 3-chlorobenzoate (3CBA) is initiated by enzymes encoded by cbaABC, an operon found on composite transposon Tn5271 of plasmid pBRC60. The cbaABC gene product CbaABC converts 3CBA to protocatechuate (PCA) and 5-Cl-PCA, which are then metabolized by the chromosomal PCA meta (extradiol) ring fission pathway. In this study, cbaA was found to possess a sigma 70 type promoter. O2 uptake experiments with whole cells and expression studies with cbaA-lacZ constructs showed that cbaABC was induced by 3CBA. Benzoate, which is not a substrate of the 3CBA pathway, was a gratuitous inducer, and CbaR, a MarR family repressor coded for by a divergently transcribed gene upstream of cbaABC, could modulate induction mediated by benzoate. Purified CbaR bound specifically to two regions of the cbaA promoter (PcbaA); site I, a high-affinity site, is between the transcriptional start point (position +1) and the start codon of cbaA, while site II, a lower-affinity site, overlaps position +1. 3CBA at concentrations as low as 40 µM interfered with binding to PcbaA. PCA also interfered with binding, while benzoate only weakly disrupted binding. Unexpectedly, benzoate with a hydroxyl or carboxyl at position 3 improved CbaR binding. Data are also presented that suggest that an unidentified regulator is encoded on the chromosome that induces cbaABC in response to benzoate and 3CBA.

* Corresponding author. Mailing address: Institute of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6. Phone: (613) 520-2600, ext. 3651. Fax: (613) 520-2569. E-mail: cwyndham{at}ccs.carleton.ca.

Applied and Environmental Microbiology, August 2001, p. 3530-3541, Vol. 67, No. 8
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.8.3530-3541.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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