Bacterial resistances to toxic metal ions--a review.
Bacterial plasmids encode resistance systems for toxic metal ions, including Ag+, AsO2-, AsO4(3-), Cd2+, Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, Sb3+, TeO3(2-), Tl+ and Zn2+. The function of most resistance systems is based on the energy-dependent efflux of toxic ions. Some of the efflux systems are ATPases and others are chemiosmotic cation/proton antiporters. The Cd(2+)-resistance ATPase of Gram-positive bacteria (CadA) is membrane cation pump homologous with other bacterial, animal and plant P-type ATPases. CadA has been labeled with 32P from [alpha-32P] ATP and drives ATP-dependent Cd2+ (and Zn2+) uptake by inside-out membrane vesicles (equivalent to efflux from whole cells). Recently, isolated genes defective in the human hereditary diseases of copper metabolism, namely Menkes syndrome and Wilson's disease, encode P-type ATPases that are more similar to bacterial CadA than to other ATPases from eukaryotes. The arsenic resistance efflux system transports arsenite [As(III)], alternatively using either a double-polypeptide (ArsA and ArsB) ATPase or a single-polypeptide (ArsB) functioning as a chemiosmotic transporter. The third gene in the arsenic resistance system, arsC, encodes an enzyme that converts intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. The triple-polypeptide Czc (Cd2+, Zn2+ and Co2+) chemiosmotic efflux pump consists of inner membrane (CzcA), outer membrane (CzcC) and membrane-spanning (CzcB) proteins that together transport cations from the cytoplasm across the periplasmic space to the outside of the cell.
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Department of Microbiology and Immunology, University of Illinois at Chicago 60612-7344, USA. U20053@uicvm.uic.edu
D004352:Drug Resistance, Microbial; D005798:Genes, Bacterial; D006090:Gram-Negative Bacteria / Q000235:genetics / Q000378:metabolism*; D006094:Gram-Positive Bacteria / Q000235:genetics / Q000378:metabolism*; D006527:Hepatolenticular Degeneration / Q000235:genetics; D006801:Humans; D016623:Ion Pumps / Q000235:genetics / Q000378:metabolism*; D007706:Menkes Kinky Hair Syndrome / Q000235:genetics; D008670:Metals / Q000378:metabolism / Q000633:toxicity*; D019216:Metals, Heavy / Q000378:metabolism / Q000633:toxicity; D010957:Plasmids
D016623:Ion Pumps; D008670:Metals; D019216:Metals, Heavy