Cadmium toxicity and mutagenicity in excision repair deficient and Cadmium toxicity and mutagenicity in excision repair deficient and proficient strains of proficient strains of Salmonella typhimuriumSalmonella 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 CdCl2, toxicity Was absent. Among numerous normal size colonies, a few small colonies were also observed.

0.003 0.002 0.002 0.001

0.18 0.160.21 0.23

0

No.

of

cells

X10

0 m

illio

n.

NormalSmall

Micro moles of Cadmium.

.0 3.3 33 330

Cadmium toxicity in excision repair deficient strain: Normal and Small colonies.

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.

NormalSmall

X108 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 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.

0 100 5000

0

Micro moles of Cadmium

14.7

0.04

13.5

0.002

0.0003

NormalSmall

X108 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.

NormalSmall

X108 cells

0 100 2500 5000

Micro moles of Cadmium.

0smallnormal

10.9

0.0000030.0

Discussion

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.

Acknowledgements

● We thank financial support from the NIH Bridges Program.