title: Identification and functional characterization of CbaR, a MarR-like modulator of the cbaABC-encoded chlorobenzoate catabolism pathway.
abstract: 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. O(2) 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 (P(cbaA)); 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 microM interfered with binding to P(cbaA). 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.
authors.affiliation: Institute of Biology, Carleton University, Ottawa, Ontario, Canada K1S 5B6.
authors.forename: M A
authors.initials: MA
authors.lastname: Providenti
authors.forename: R C
authors.initials: RC
authors.lastname: Wyndham
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002723:Chlorobenzoates / Q000378:metabolism*; D020604:Comamonas testosteroni / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018983:DNA Footprinting; D003851:Deoxyribonucleases / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; C437394:CbaR protein, Comamonas testosteroni; D002723:Chlorobenzoates; D029968:Escherichia coli Proteins; C080004:MarR protein, E coli; D012097:Repressor Proteins; C036427:3-chlorobenzoic acid; D003851:Deoxyribonucleases