CADMIUM TOXICITY AND RESISTANCE IN CHLORELLA SP

The Cd2+ tolerance of Chlorella sp. isolated from an urban waste water treatment plant was studied. The growth of this alga was severely inhibited at 10 mu M Cd2+ With an LD(50) of 3 mu M. Addition of 100 mu M glutathione or 100 mu M cysteine reduced the inhibitory effect of Cd2+. The amelioration of Cd2+ inhibition by GSH was;lot due to direct complexing of the two compounds in the growth medium, indicating that an intracellular mechanism involving GSH or its metabolites is responsible for Cd2+ detoxification. A Cd2+ resistant line (CdR-DK), with an LD(50) of 35 mu M, was selected by growing the alga on solid medium in the presence of increasing concentrations of the ion. Phytochelatins (PCs), a family of peptides synthesized by plants in response to cadmium, were detected in extracts of the CdR-DK cells. The possible role that these peptides, which are derived from glutathione, may play in cadmium detoxification in Chlorella is discussed.