Journal of Industrial Microbiology & Biotechnology (1998) 20 , 1–12  1998 Society for Industrial Microbiology 1367-5435/98/$12.00 Genes for all metals—a bacterial view of the Periodic Table The 1996 Thom Award Lecture S Silver Department of Microbiology and Immunology, University of Illinois, Chicago, IL 60612-7344, USA Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH + 4 ,K + , Mg 2+ , Co 2+ , Fe 3+ , Mn 2+ , Zn 2+ and other trace cations, and PO 3- 4 , SO 2- 4 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 + , AsO - 2 , AsO 3- 4 , Cd 2+ , Co 2+ , CrO 2- 4 , Cu 2+ , Hg 2+ , Ni 2+ , Pb 2+ , TeO 2- 3 , TI + and Zn 2+ . 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 32 P from [- 32 P]ATP and drives ATP-dependent Cd 2+ (and Zn 2+ ) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson’s dis- ease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system trans- ports 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 Cd 2+ , Zn 2+ and Co 2+ . This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane- spanning (CzcB) protein that function together. Keywords: bacterial plasmids; toxic metal resistances; mercury; cadmium; arsenic Charles Thom Charles Thom, whose achievements we honor in this lec- ture series, was the first President of the Society of Indus- trial Microbiology, from 1949–1951. He had been earlier President of the Society of American Bacteriologists (later renamed the American Society for Microbiology) and was a member of the National Academy of Sciences. Charles Thom was born and raised on a farm near Peoria, Illinois, and after bachelors and masters degrees from a small col- lege north of Chicago, he obtained the first PhD awarded at the University of Missouri (in 1899). Dr Thom worked essentially his entire professional career with the US Department of Agriculture (USDA), from 1902 until retire- ment in 1942, mostly in Washington, DC, but he then con- tinued to work with the penicillin development program at the USDA Northern Regional Research Laboratories (NRRL) at Peoria for another 10 years. During this long service, Dr Thom had several major achievements—more than most scientists expect. His first assignment was to bring a quality mold-ripened cheese industry from France to the USA. This required fungal tax- onomy and he identified and named Penicillium camerberti and Penicillium roqueforti. Dr Thom became the major mycologist/taxonomist of his time and wrote (with collaborators) monographs on the genera Penicillium and Aspergillus in the 1920s that were updated and remained Correspondence: S Silver, Department of Microbiology and Immunology, University of Illinois at Chicago, M/C 790, Room 703, 835 S Wolcott Avenue, Chicago, IL 60612-7344, USA Received 8 August 1997; accepted 1 November 1997 standard into the 1940s. Although he remained a mycol- ogist with strong applied and theoretical interests, the USDA used Dr Thom’s abilities for quite different enterprises. He helped develop the pure food and drug stan- dards that became the basis for the Food and Drug Admin- istration (FDA), which grew out from the USDA. Dr Thom appeared in court hearings, laying down production stan- dards for the food processing industry. He wrote an early standard text on food microbiology. Next he helped to place soil microbiology on a solid scientific footing. With a col- league, he developed the first industrial fermentation of cit- ric acid (by Aspergillus niger). This led to the establishment of a Fermentation Division and Fungal Culture Collection at the NRRL in Peoria. When during World War II, a Brit- ish delegation trying to involve the American fermentation industry in developing penicillin ran into disinterest and lack of understanding, they visited Dr Thom in Washington DC with their problems. The USDA NRRL played a major role in the history of penicillin production. He maintained interests in fungal applications until his death at age 84 in 1956. Although he worked within government, Charles Thom was well known for encouraging younger co-workers. This section was written from material of his best-known ‘junior assistant’, Kenneth B Raper [58,59], who was associated with Dr Thom from college graduation through the remain- der of Dr Thom’s time in the laboratory. Introduction Bacteria have genes specific for transport of needed nutri- ents and for resistances to the toxic ions of most heavy