Bacterial Heavy Metal Detoxification and Resistance Systems

  • Simon Silver


Bacterial plasmids contain genetic determinants for resistance systems for Hg2+ (and organomercurials), Cd2+, AsO2, AsO4 3-, CrO4 2-, TeO3 2-, Cu2+, Ag+, Co2+, Pb2+, and other metals of environmental concern. In some cases, there is the potential for using genetically engineered microbes for bio-remediation. Recombinant DNA analysis has been applied to mercury, cadmium, zinc, cobalt, arsenic, chromate, tellurium and copper resistance systems. The eight mercury resistance systems that have been sequenced all contain the gene for mercuric reductase, the enzyme that converts toxic Hg2+ ions to less toxic volatile metallic Hg°. Four of these systems also determine the enzyme organomercurial lyase, which cuts the HgC bond and thus detoxifies methylmercury and phenylmercury. Two sequenced Cd2+ resistance determinants govern cellular efflux of Cd2+ assuring a low level of intracellular Cd2+: not an obvious candidate for bioremediation. Cadmium accumulation by bacterial metallothionein or phytochelatin is a potentially useful process, but only preliminary reports have appeared on bacteria producing polythiol polypeptides. For arsenic resistance, a unique efflux ATPase maintains low intracellular As levels. A bacterial AsO2- oxidase has been reported, with the potential of converting more toxic As(III) into less toxic As(V), but this system has not been studied in recent years. For chromate, resistance results from reduced cellular uptake. However, both soluble and membrane-bound Cr(VI) reductase bacterial activities convert more toxic Cr(VI) to less toxic Cr(III) in different bacteria.


Resistance System Resistance Determinant Copper Resistance Chromate Reduction Chromate Resistance 
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© Plenum Press, New York 1992

Authors and Affiliations

  • Simon Silver
    • 1
  1. 1.University of IllinoisChicagoUSA

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