title: CadA of Mesorhizobium metallidurans isolated from a zinc-rich mining soil is a P(IB-2)-type ATPase involved in cadmium and zinc resistance.
abstract: Mesorhizobium metallidurans STM 2683(T) is a nitrogen-fixing bacterium that nodulates Anthyllis vulneraria in mine tailings highly contaminated in zinc, lead and cadmium. To study the mechanisms whereby this bacterium copes with metals, we functionally screened a cosmid genomic library of M. metallidurans for zinc or cadmium tolerance. A cosmid clone harbored a gene encoding P(IB)-type ATPase homologous to CadA that leads to cadmium and zinc resistance in Escherichia coli. The CadA protein structure presents one duplication of the two N-terminal metal binding domains (i.e. a heavy metal-associated domain followed by a histidine-rich domain) which allows specific binding to zinc and cadmium cations. A cadA-deleted strain of M. metallidurans failed to grow at high zinc concentrations (2 mM) and its growth was delayed at lower zinc concentrations. Expression studies using a transcriptional fusion of cadA promoter to gfp showed that cadA is specifically induced in a dose-dependent manner by zinc and cadmium in M. metallidurans in vitro conditions and into A. vulneraria nodules after Zn stress. Metal induction sensitivity was increased in the strain where cadA gene was deleted. This study identified cadA as a first mesorhizobial resistance determinant involved in detoxification of cadmium and zinc and which confers upon M. metallidurans greater capacity for coping with high zinc concentrations. This improves the knowledge of this bacterium for potential use as a symbiotic inoculant of Anthyllis in phytostabilization strategies of metal-rich sites.
authors.affiliation: INRA USC1242, Université Montpellier II, TA A-82/J, 34398 Montpellier Cedex 5, France. Electronic address: geraldine.maynaud@ird.fr.
authors.forename: Geraldine
authors.initials: G
authors.lastname: Maynaud
authors.affiliation: Montpellier SupAgro, Université Montpellier II, TA A-82/J, 34398 Montpellier Cedex 5, France. Electronic address: brunel@supagro.inra.fr.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Brunel
authors.affiliation: Montpellier SupAgro, Université Montpellier II, TA A-82/J, 34398 Montpellier Cedex 5, France. Electronic address: erika.yashiro@unil.ch.
authors.forename: Erika
authors.initials: E
authors.lastname: Yashiro
authors.affiliation: Molecular and Cellular Biology, Unit Microbiology, Belgian Nuclear Research Center (SCK CEN), Boeretang 200, B-2400 Mol, Belgium. Electronic address: mmergeay@sckcen.be.
authors.forename: Max
authors.initials: M
authors.lastname: Mergeay
authors.affiliation: INRA USC1242, Université Montpellier II, TA A-82/J, 34398 Montpellier Cedex 5, France. Electronic address: cleyet@supagro.inra.fr.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Cleyet-Marel
authors.affiliation: IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes UMR113, IRD/INRA/CIRAD/Montpellier SupAgro/Université Montpellier II, TA A-82/J, 34398 Montpellier Cedex 5, France. Electronic address: antoine.le-quere@ird.fr.
authors.forename: Antoine
authors.initials: A
authors.lastname: Le Quéré
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002104:Cadmium / Q000633:toxicity*; D024881:Drug Resistance, Bacterial; D007887:Fabaceae / Q000382:microbiology; D017353:Gene Deletion; D020869:Gene Expression Profiling; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000032:analysis; D059128:Mesorhizobium / Q000201:enzymology* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D055170:Plant Root Nodulation; D011485:Protein Binding; D016415:Sequence Alignment; D012988:Soil Microbiology; D015032:Zinc / Q000633:toxicity*
chemical_list: D002104:Cadmium; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases; C059771:cadmium translocating ATPase; D015032:Zinc
keywords: Mesorhizobium; Metal efflux transporter; Metal tolerance; P(IB)-type ATPase; cadA transcription