1. Cadmium toxicity and mutagenicity in excision repair deficient and proficient strains of Salmonella typhimurium Kip Green, Gyula Ficsor, and Leonard Ginsberg, Biological Sciences Department Western Michigan University, Kalamazoo, MI Introduction ● Cadmium is a naturally occurring metallic element, and is ubiquitous in the environment. ● It is taken up by plants, e.g. tobacco. ● It has no beneficial biologic role. ● Ouch-ouch disease in Japan. ● Devastating to male fertility in mice. Hypothesis At high doses Cadmium replaces Zinc in an S.O.S. repair protein. Methods & Materials ● S. typhimurium is treated with Cadmium Chloride. ● After 24hrs, the cells were washed and plated. ● After incubation @ 37.5 Celsius for 24 hrs. colonies were counted and were observed for colony size. Excision repair deficient and proficient strains used. ● The excision repair deficient strains can not repair DNA damage during DNA replication (first line of defense) ● The excision repair proficient strain can repair DNA replication DNA damage. Results Normal and Small colonies: excision repair deficient, control Normal and Small colonies: excision repair deficient, Cd-treated Normal and Small colonies: excision repair proficient, Cd-treated Toxicity of Cadmium Chloride in the excision repair deficient strain. Normal and Small colonies. In the zero to 300 micro mole range of CdCl 2, toxicity Was absent. Among numerous normal size colonies, a few small colonies were also observed. 0.003 0.002 0.001 0.18 0.16 0.21 0.23 0 No. of cells X 100 million. Normal Small Micro moles of Cadmium.. 0 3.333330 Cadmium toxicity in excision repair deficient strain: Normal and Small colonies. 10 & 100 micro moles of CdCl 2 were not toxic, and there were more normal colonies than small colonies. At 5000 micro moles CdCl 2 was toxic, and there were more small colonies than normal colonies. Normal Small X10 8 cells : Micro moles of Cadmium. 0 10 100 5000 Normal Small 9.7 10.5 8.6 0.0 0.0003 0.0013 Cadmium toxicity in excision repair deficient strain. (repeat experiment.) 10 & 100 micro moles CdCl 2 were not toxic. 5000 micro moles of CdCl 2 was toxic. At the more toxic dosage, At 5000 micro moles CdCl 2 was toxic, and there were more small colonies than normal colonies. 0 100 5000 0 Micro moles of Cadmium 14.7 0.04 13.5 0.002 0.0003 Normal Small X10 8 cells : Toxicity of Cadmium Chloride in excision repair proficient strain. At 2500 to 5000 micro moles of Cadmium, normal colonies are more frequent than small colonies. Normal Small X10 8 cells 0 100 2500 5000 Micro moles of Cadmium. 0 small normal 10.9 0.000003 0.0 Discussion CdCl 2 was not toxic over a range of 3.3 and 330 micro moles. Cell killing is more than 99.9% at doses of 2500 micro moles to 5000 micro moles. At high doses, many slow growing (small) mutant colonies were seen in the excision repair deficient strain. In the absence of excision repair, cell survival depends on the SOS repair. We suggest that at high doses, Cd replaces zinc in a SOS protein and causes a higher level of mutations (small) then would be the case if Zinc was present. This hypothesis is supported by the fact that when excision repair is present, and the SOS repair is absent, fewer mutations are induced. Acknowledgements ● We thank financial support from the NIH Bridges Program.