Cadmium toxicity and mutagenicity in excision repair deficient and proficient strains of Salmonella typhimurium

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
Results
Introduction
Toxicity of Cadmium Chloride in the excision
repair deficient strain. Normal and Small
colonies.
Toxicity of Cadmium Chloride in excision repair
proficient strain.
? 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.
Normal and Small colonies excision repair
deficient, control
X108 cells
Normal
Small
0
3.3
33
330
Hypothesis
At 2500 to 5000 micro moles of Cadmium, normal
colonies are more frequent than small colonies.
At high doses Cadmium replaces Zinc in an S.O.S.
repair protein.
Cadmium toxicity in excision repair deficient
strain Normal and Small colonies.
Discussion
Methods Materials
Normal and Small colonies excision repair
deficient, Cd-treated
10.5
9.7
CdCl2 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.
X108 cells
8.6
? S. typhimurium is treated with Cadmium
Chloride. ? After 24hrs, the cells were
washed and plated. ? After incubation _at_
37.5 Celsius for 24 hrs. colonies were
counted and were observed for colony
size.
Normal
0.0
Small
0.0013
Small
0.0003
Normal
0
10
100
5000
Micro moles of Cadmium.
10 100 micro moles of CdCl2 were not toxic, and
there were more normal colonies than small
colonies. At 5000 micro moles CdCl2 was toxic,
and there were more small colonies than normal
colonies.
Excision repair deficient and proficient strains
used.
Normal and Small colonies excision repair
proficient, Cd-treated
Cadmium toxicity in excision repair deficient
strain. (repeat experiment.)
Acknowledgements
X108 cells
? We thank financial support from the NIH
Bridges Program.
Normal
? 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.
Small
10 100 micro moles CdCl2 were not toxic. 5000
micro moles of CdCl2 was toxic. At the more toxic
dosage, At 5000 micro moles CdCl2 was toxic, and
there were more small colonies than normal
colonies.