Date of Defense

Summer 8-7-1998


Biological Sciences

First Advisor

Silvia Rossbach, Biological Sciences

Second Advisor

David Reinhold, Chemistry

Third Advisor

Barbara Cockrell, Biological Sciences


One side effect of today's industrialized world is increased levels of heavy metals in the environment. Many of these metals are necessary for biological function as trace elements, but at higher concentrations are toxic. Other metals, such as cadmium, are not beneficial at any level, and have only deleterious effects on living organisms. Cadmium is primarily thought to interfere with normal biological function of proteins. Human exposure to cadmium appears to primarily damage the kidneys, but may also affect the liver, lungs, immune system, and central nervous system. Bacteria, however, have developed several methods for handling toxic heavy metals: cation efflux from the cell, sequestration of metals in compartments within the cell, exclusion from entering the cell, and transformation of the metals to a less toxic valence state. The genes enabling metal resistance are usually located on plasmids, but some resistance genes are found on the chromosome. Sequencing work has revealed several chromosomal genes with homology to known plasmid metal resistance genes, indicating these plasmids have exchanged genes with the genome on occasion. Soil bacteria such as Pseudomonas fluorescens are among the first organisms to be exposed to metal wastes released into the environment. The goal of this study was to characterize chromosomal cadmium resistance in P. fluorescens. Previously, 17 mutant strains had been created through transposon mutagenesis, which used the E. coli lacZ gene as a reporter for gene activity. This study further characterizes these 17 strains using several methods: the strains were grown under many stressful conditions to determine if their differential gene activity was specific to cadmium or a general response; quantitative assays were performed to yield dose-responsive curves for β-galactosidase activity with varying cadmium levels; an attempt was made to clone and map the tagged genes as a first step towards sequencing.

Access Setting

Honors Thesis-Open Access