INTERACTION OF LEAD NITRATE AND CADMIUM CHLORIDE WITH ESCHERICHIA-COLI K-12 AND SALMONELLA-TYPHIMURIUM GLOBAL REGULATORY MUTANTS

To investigate the interactions of heavy metals with cells, a minimal medium for the growth of enteric bacteria using glycerol-2-phosphate a s the sole phosphorus source was developed that avoided precipitation of Pb2+ with inorganic phosphate. Using this medium, spontaneous mutan ts of Escherichia coli resistant to addition of Pb(NO3)(2) were isolat ed. Thirty-five independent mutants all conferred a low level of resis tance. Disk diffusion assays on solid medium were used to survey the r esponse of E. coli and Salmonella typh,nltriilm mutants altered in glo bal regulatory networks to Pb(NO3)(2) and CdCl2. Strains bearing mutat ions in axyR and rpoH were the most hypersensitive to these compounds. Based upon the response of strains completely devoid of isozymes need ed to inactivate reactive oxygen species, this hypersensitivity to lea d and cadmium is attributable to alteration in super oxide dismutase r ather than catalase levels. Similar analysis of chaperone-defective mu tants suggests that these metals damage proteins in vivo.