CADMIUM TOXICITY ON THE FRESHWATER MICRO ALGA CHLAMYDOMONAS MOEWUSII GERLOFF: BIOSYNTHESIS OF THIOL COMPOUNDS

摘要

Cadmium (Cd) toxicity and production of different thiols (phytochelatins, glutathione, 7-Glu-Cys and cysteine) were studied in the microalga Chlamydomanas moewusii exposed to different concentrations of this metal (1, 2, 4, 6, 8, and 10 mg/L) for 96 h. The inhibitory effect of Cd on growth was demonstrated. The value of EC50 (metal concentration which reduces the population growth to 50% of the control) obtained for this microalga was estimated at 4.1 ±0.8 mg/L of Cd after 96h of exposure. The amount of thiol compounds synthesized by C. moewusii changed with Cd concentration. Cysteine concentrations were significantly higher compared to those of γ-Glu-Cys and glutathione in all the Cd concentrations assayed. The amino acid cysteine reached its higher levels in those cultures in which a decrease in the concentration of phytochelatins (PCs) was observed. Both cysteine and glutathione concentrations showed significant differences along the Cd concentrations assayed, while the amount of γ-Glu-Cys detected remained stable. The PCs detected were of two, three, and four subunits. The level of PC_2 was higher than that of PC_3 and PC_4. PC_4 was detected only in the cultures exposed to the Cd concentrations of 1 and 2 mg/L, in which the synthesis of phytochelatins was higher. A rapid increase in the production of PC_2 and PC_3 was observed up to a Cd concentration of 2 mg/L, after which their levels began to decrease. Phytochelatins were not detected in cultures without Cd (controls) and in those exposed to the maximum Cd concentration (10 mg/L), in which cell growth was completely inhibited.