Cell free mercury (II) reducing activity in a plasmid bearing strain of Escherichia coli

Abstract

The ability to reduce Hg(II) to Hg(0), which is determined by a plasmid borne gene in E. coli, is conferred by a Hg(II) inducible activity which is located in the cytoplasm rather than in the periplasmic space of the cell. This Hg(II) reducing activity can be isolated from the supernatant of a 160,000 x g centrifugation after French Press disruption of the cells. The activity is dependent on glucose 6 phosphate, glucose 6 phosphate dehydrogenase, and 2 mercaptoethanol, but is not enhanced by added nicotinamide adenine dinucleotide phosphate. Treatment of the active fraction with N ethylmaleimide causes irreversible loss of the Hg(II) reducing activity. Unlike the Hg(II) reducing activity found in intact cells, the cell free activity is not inhibited by toluene, potassium cyanide, or m chlorocarbonylcyanide phenylhydrazone; however, it is inhibited by Ag(I) and phenylmercuric acetate to the same extent as the activity in intact cells. Neither phenylmercuric acetate nor methylmercuric chloride is reduced to Hg(0) by the cell free activity. Au (III), however, is a substrate for the cell free activity; it is reduced to metallic colloidal Au(0).