Antagonisms between cadmium and zinc toxicity and manganese limitation in a coastal diatom

Long-term growth and metal (Mn and Cd) uptake experiments and short-term uptake kinetic experiments with the coastal diatom Thalassiosira pseudonana revealed antagonistic interactions between toxic metals (Zn and Cd) and the micronutrient manganese. Cd and Zn inhibited algal growth rate only at low Mn ion concentrations, an effect that could be totally accounted for by an inhibition of cellular Mn uptake by the toxic metals and the resultant generation of Mn-deficient cells. Mn and Zn inhibited cellular Cd uptake, indicating reciprocal effects among the metals with respect to uptake. Saturation kinetics modeling of the uptake data was consistent with all three metals competing with each other for binding to the Mn uptake system and with both Cd and Mn being transported into the cell by that system (uptake of Zn was not measured). Mathematical modeling of Mn and Cd uptake data revealed evidence for a Cd efflux system that was induced only at high cellular Cd concentrations and prevented cellular Cd from reaching toxic levels.