Bacterial resistances to toxic metal ions - a review |
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Institution: | 1. School of Environmental Studies, China University of Geosciences (Wuhan), Wuhan 430074, China;2. State Key Laboratory of Biogeology and Environmental Geology, China University of China (Wuhan), Wuhan 430074, China;1. Shandong Provincial Key Laboratory of Applied Microbiology, Ecology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250013, China;2. Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China |
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Abstract: | Bacterial plasmids encode resistance systems for toxic metal ions, including Ag+, AsO2-, AsO43-, Cd2+, Co2+, CrO42-, Cu2+ Hg2+, Ni2+, Pb2+, Sb3+, TeO32-, 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 Cd2+-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 α-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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