In the natural environment, toxicant effects can be monitored by the signature mRNA expression patterns of genes that they generate in test organisms. The specificity and sensitivity of these transcriptome-based bioassays to a given toxicant can be confounded by temporal changes in biomarker mRNA expression, effects of other toxicants and hardness ions, and non-linear mRNA expression responses of genes. This study provides the foundation for the development of a transcriptomic-based bioassay for bioavailable Cd in the freshwater alga, Chlamydomonas reinhardtii. It characterizes: (1) the Cd regulation of nine genes with respect to their mRNA induction kinetics; (2) the effects of two additional metals common to freshwaters, Cu2+ and Pb2+, and (3) the relationships between metal bioaccumulation and the transcriptomic responses. Quantitative real time PCR was used to monitor mRNA levels of nine Cd-induced genes following an exposure to 0.01, 0.11 and 1.16 μM Cd2+. Several distinct mRNA expression patterns were observed with time. While the presence of Cu2+ and Pb2+ decreased Cd biouptake, mRNA levels increased for six genes, showing lack of Cd2+ specificity. Nonetheless, the transcriptomic effects of binary metal exposures rarely adhered to a simple additive model based on single metal exposures; rather most exhibited synergistic or antagonistic interactions. While none of these genes could be used as a specific Cd biomarker, the signature mRNA expression profile obtained from a select subset of Cd sensitive genes was a useful biomarker of sublethal effects.
2010 Elsevier B.V. All rights reserved.