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Applied and Environmental Microbiology, April 2001, p. 1437-1444, Vol. 67, No. 4
Department of Plant Pathology, University of
California, Riverside, California 92521-0122
Received 10 October 2000/Accepted 9 January 2001
Pseudomonads from environmental sources vary widely in their
sensitivity to cadmium, but the basis for this resistance is largely
uncharactarized. A chromosomal fragment encoding cadmium resistance was
cloned from Pseudomonas putida 06909, a rhizosphere bacterium, and sequence analysis revealed two divergently transcribed genes, cadA and cadR. CadA was similar to
cadmium-transporting ATPases known mostly from gram-positive
bacteria, and to ZntA, a lead-, zinc-, and cadmium-transporting ATPase
from Escherichia coli. CadR was related to the MerR family
of response regulators that normally control mercury detoxification in
other bacterial systems. A related gene, zntR, regulates
zntA in E. coli, but it is not contiguous with
zntA in the E. coli genome as cadA
and cadR were in P. putida. In addition, unlike
ZntA and other CadA homologs, but similar to the predicted product of
gene PA3690 in the P. aeruginosa genome, the P. putida CadA sequence had a histidine-rich
N-terminal extension. CadR and the product of PA3689 of P. aeruginosa also had histidine-rich C-terminal extensions not found in other MerR family response regulators. Mutational analysis
indicated that cadA and cadR are fully
responsible for cadmium resistance and partially for zinc resistance.
However, unlike zntA, they did not confer significant
levels of lead resistance. The cadA promoter was responsive
to Cd(II), Pb(II), and Zn(II), while the cadR promoter was
only induced by Cd(II). CadR apparently represses its own expression at
the transcriptional level. However, CadR apparently does not repress
cadA. Homologs of the cadmium-transporting ATPase were
detected in many other Pseudomonas species.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1437-1444.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Chromosomal Locus for Cadmium Resistance in Pseudomonas
putida Consisting of a Cadmium-Transporting ATPase and a
MerR Family Response Regulator

and
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Corresponding author. Mailing address: Department
of Plant Pathology-071, 237 Webber Hall, University of
California, Riverside, CA 92521-0122. Phone: (909) 787-3516. Fax: (909)
787-4294. E-mail: Cooksey{at}citrus.ucr.edu.
Present address: Korea Research Institute of Chemical Technology,
Yusong, Taejon 305-600, Korea.
Present address: IPK (Institut für Pflanzengenetik und
Kulturpflanzenforschung), Molecular Plant Physiology group,
Gatersleben, Germany.
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