title: Genes for all metals--a bacterial view of the periodic table. The 1996 Thom Award Lecture.
abstract: Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH4+, K+, Mg2+, Co2+, Fe3+, Mn2+, Zn2+ and other trace cations, and PO4(3-), SO4(2-) and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids encode resistance systems for toxic metal and metalloid ions including Ag+, AsO2-, AsO4(3-), Cd2+, Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, TeO3(2-), Tl+ and Zn2+. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations. Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd(2+)-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with 32P from [gamma-32P]ATP and drives ATP-dependent Cd2+ (and Zn2+) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson's disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides, ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex functions as a chemiosmotic cation/protein exchanger to efflux Cd2+, Zn2+ and Co2+. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function together.
authors.affiliation: Department of Microbiology and Immunology, University of Illinois, Chicago 60612-7344, USA.
authors.forename: S
authors.initials: S
authors.lastname: Silver
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D001363:Awards and Prizes; D001419:Bacteria / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002876:Chromosomes, Bacterial / Q000235:genetics*; D004352:Drug Resistance, Microbial / Q000235:genetics; D016680:Genome, Bacterial; D049673:History, 20th Century; D019216:Metals, Heavy / Q000378:metabolism / Q000494:pharmacology*; D009172:Mycology / Q000266:history; D011815:R Factors / Q000235:genetics; D014481:United States
chemical_list: D002352:Carrier Proteins; D019216:Metals, Heavy; D000251:Adenosine Triphosphatases