Abstract

Toxic trace metals are major environmental pollutants due to their high toxicity at low concentrations, non-biodegradability, and accumulation in the food chain. Metals are important pollutants from metal mining, a major industry in Canada. Therefore, effective means of toxic trace metal quantification in natural water and soils are required for environmental risk assessment. Although analytical chemistry provides highly accurate and precise methods for quantifying metals, complete environmental risk assessment requires a determination of whether or not a metal is bioavailable, i.e. present in toxic or benign species. Of these toxic trace metals, our focus was on Cd as it is considered to be one of the most toxic heavy metals at sublethal concentrations. The absolute Cd concentration in natural waters does not necessarily reflect the concentration of a metal that is bioavailable. Therefore, analytical methods need to be complemented with bioassays (organisms that report the presence of bioavailable metal. This thesis contributes to the development of two types of cadmium (Cd) bioassays using the green alga Chlamydomonas reinhardtii. These bioassays are intended to detect trace amounts of the bioavailable species of cadmium (Cd). Previous global transcriptome studies by Simon et al. identified 10 Cd genes that are
IV
induced by Cd2+exposure at concentrations in micromolar range. We focused on a gene encoding a predicted amino acid transporter (AOT4) because it had the highest level of induction at low [Cd2+] (1.2 μM). Reporter genes were constructed using the promoter region of this gene. Validation of the promoter region was based on Northern blot experiments. Another method used the technology of Panomics Inc. that allowed for direct quantitation of AOT4 mRNA levels. I established 2 Panomics assays and optimized them so that they could be used with C. reinhardtii. The goal of these bioassays is to make them specific and respond to environmentally relevant Cd concentrations and allow use of sensitive, simple, portable equipment for in situ Cd measurements