Isolation of Cadmium- and Mercury-sensitive Mutants of Escherichia coli and Some Factors Influencing Their Sensitivities

Several Cd²⁺ hypersensitive and Hg²⁺ sensitive mutants of Escherichia coli K-12 were isolated after repeated mutagenesis with nitrosoguanidine. The Cd-hypersensitive mutant, CD17P, could not grow in a chemically defined liquid medium containing 0.5 μm Cd²⁺, and the growth of Hg-sensitive mutant, HG17P-52, was inhibited by 0.9 μm Hg²⁺. Thus, CD 17P and HG17P-52 were respectively about 1000 fold and 4 fold more sensitive than the parental strain.

Both mutants were also considerably more sensitive to Zn²⁺ than their parent, but they did not show any appreciable change in sensitivity to other metals tested. Among the various metabolites and chemicals tested, reducing agents such as cysteine, dithiothreitol and vitamin C showed a protective effect against metal toxicity. Reduced glutathione was effective only against Hg²⁺. EDTA specifically and efficiently reversed only Cd²⁺ toxicity.