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.
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
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.
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