MT-like proteins: Potential bio-indicators of Chlorella vulgaris for zinc contamination in water environment

Chlorella vulgaris has been usually used to monitor the toxicity of Zn in water environment, but the biochemical responses of the algae to Zn2+ at different levels remain unknown to date. In the present study, the growth inhibition, the antioxidant enzymes, the subcellular Zn and the induced Zn-metallothionein-like (Zn-MT-like) proteins in C. vulgaris exposed to 0, 5, 10, 20, 50 and 100 μmol l−1 of Zn2+ were investigated. Results showed that the growth of C. vulgaris was significantly inhibited (p < 0.05) at Zn2+ level above 5 μmol l−1. Compared with the control group, the activities of peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase mostly increased with the rises of Zn2+ concentrations ranging from 5 to 100 μmol l−1, except for GSH-Px with a lower value in the 100 μmol l−1 group compared with that of the 50 μmol l−1 group, and SOD with no significant difference at the 5, 10 and 100 μmol l−1 groups compared with that of the control group. Contrarily, the activities of guaiacol peroxidase significantly decreased (p < 0.05) at Zn2+ concentrations from 5 to 100 μmol l−1 compared with that of the control group. After 72 h exposure, Zn in the algal cells was observed to mainly distribute in the form of heat stable fractions, in which Zn-binding metallothionein-like (MT-like) proteins were largely biosynthesized. In addition, the amounts of Zn-MT-like proteins induced in the algae significantly increased (p < 0.05) with the rises of Zn2+ concentrations at the assay levels. The results indicated that the activities of antioxidant enzymes and the induction of Zn-MT-like proteins in C. vulgaris may play important roles in dealing with the toxicity of Zn2+ to the algal cells, and the induction of Zn-MT-like proteins in C. vulgaris can be used as a potential bio-indicator to monitor the contamination of Zn2+ in water environment.