Affiliation:
1. Department of Applied Chemistry and Microbiology, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland
2. Laboratory of Molecular Genetics, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Abstract
ABSTRACT
According to in silico analysis, the genome of
Pseudomonas putida
KT2440 encodes at least four Zn/Cd/Pb efflux transporters—two P-type ATPases (CadA1 and CadA2) and two
czc
chemiosmotic transporters (CzcCBA1 and CzcCBA2). In this study we showed that all these transporters are functional, but under laboratory conditions only two of them were involved in the mediation of heavy metal resistance in
P. putida
KT2440. CadA2 conferred Cd
2+
and Pb
2+
resistance, whereas CzcCBA1 was involved in export of Zn
2+
, Cd
2+
, and possibly Pb
2+
. CadA1, although nonfunctional in
P. putida
, improved Zn
2+
resistance and slightly improved Cd
2+
resistance when it was expressed in
Escherichia coli
. CzcCBA2 contributed to Zn resistance of a
czcA1
-defective
P. putida
strain or when the CzcA2 subunit was overexpressed in a transporter-deficient strain. It seemed that CzcA2 could complex with CzcC1 and CzcB1 subunits and therefore complement the loss of CzcA1. The CzcCBA2 transporter itself, however, did not function. Expression of
cadA1
,
cadA2
, and
czcCBA1
was induced by heavy metals, and the expression levels were dependent on the growth medium and growth phase. Expression of
cadA2
and
czcCBA1
was nonspecific; both genes were induced by Zn
2+
, Cd
2+
, Pb
2+
, Ni
2+
, Co
2+
, and Hg
2+
. On the other hand, remarkably, expression of
cadA1
was induced only by Zn
2+
. Possible roles of distinct but simultaneously functioning transporters are discussed.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
101 articles.
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