Simultaneous Cd²⁺, Zn²⁺, and Pb²⁺ Uptake and Accumulation by Photosynthetic Euglena gracilis
2006
Mendoza-Cózatl, D. G. | Rangel-González, E. | Moreno-Sánchez, R.
The ability of Euglena gracilis to simultaneously remove and accumulate Zn²⁺, Cd²⁺, and Pb²⁺ from culture up- to media was evaluated. E. gracilis was able to remove up to 80% of the Cd²⁺ present in the medium when cultured with 20 or 50 μM CdCl₂. Higher external Cd²⁺ concentrations increased Cd²⁺ accumulation per cell but decreased cell growth, thus decreasing the capacity of the cell culture to remove Cd²⁺. E. gracilis removed 70% to 80% of the Zn²⁺ present in the medium when cultured with 5 to 50 μM ZnSO₄. Zn²⁺ did not affect Cd²⁺ removal capacity. E. gracilis was much less efficient in removing Pb²⁺ (<15%) when cultured with 100 or 200 μM Pb(NO₃)₂. Moreover, Pb²⁺ decreased the efficiency to remove Cd²⁺, but it did not affect Zn²⁺ removal. Cd²⁺ induced a generalized increase in the cellular thiol compounds, including phytochelatins, and Pb²⁺ had an additive effect only at 200 μM. Zn²⁺ did not stimulate phytochelatin synthesis. Cd²⁺ and Pb²⁺ colocated in the same cytosolic high-molecular-weight fraction. Because Pb²⁺ is a weak phytochelatin inducer, competition between Pb²⁺ and Cd²⁺ for transportation across the plasma membrane and binding to phytochelatins and other thiol compounds is proposed to explain the detrimental effects of Pb²⁺ on the Cd²⁺ removal capacity of E. gracilis.
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