Date of Award





Earth and Space Science - Environmental Science Track


Earth & Space Science

First Advisor

John K. Davis


Heavy metals have become devastating environmental contaminants due to their widespread use in the manufacture of electronics, plastics, batteries and dyes. The discharge of heavy metals into the environment has caused concern about their effects on the ecosystem. Many metals are essential for growth in small amounts. However, at higher concentrations heavy metals are toxic because they bind to organic compounds. This accounts for their effects on some important parts of the cell structure, like their ability to denature protein molecules. The initial objective of this study was to find out the growth rate of E.coli and M.roseus in the presence of 1mM and 10 uM concentrations of cadmium and lead. E.coli and M.roseus were used due to their ability to grow in a controlled environment and ease of usage. The growth rates of the bacteria and viable counts were obtained via light scattering. Bacteria were grown on rich media (LB broth) as well as mineral M9 media supplemented with and without casamino acids and growth rates were compared. Another objective in this study was to identify genes in E. coli mutants that were more resistant or sensitive to cadmium. E.coli was mutagenized with a transposon to identify mutants with altered sensitivities to Cd. The growth rates of the mutants and wild type were obtained with and without Cd. Results suggest that Cd +2 , at 10^iM and 1mM concentrations as well as Pb +2 at 1mM concentration, had a significant effect on E.coli and M.roseus in all media types. Insignificant effects were found in M.roseus and E.coli growth rates when exposed to lO^iM Pb. The responses of bacteria to cadmium salts were 100 times more toxic in comparison to lead salts, suggesting slightly different biological effect of these heavy metals. The isolation of mutants resistant to specific toxic agents such as Tc and Rif antibiotics was not a very useful genetic approach in this study. It was unfortunate that it cannot be proven that real mutants were created. Instead, the donor was already cadmium sensitive, and the Rif donor appeared to be even more sensitive to cadmium and therefore behaved like a mutant. UV-light exposure, % survival, growth rates, and appearance of plasmids confirmed exactly the same behavior of Rif resistant donor and suspected mutant. Therefore it seemed like our donor strain was already a "mutant" that has very high cadmium sensitivity. A different approach was taken In order to identify E. coli genes involved with cadmium resistance, by simply increasing concentrations of Cd +2 . E.coli strain was found that is resistant to 4.5 mM Cd +2 .