Effect of cadmium on growth of euglena gracilis in the zinc‐optimum range

Effect of cadmium at concentrations between 0.01 and 1000 μg/ml on growth of Euglena gracilis was examined in the zinc‐optimum range, in which the maximum growth was obtained. The dose‐response curve relating its growth amount to the concentration of cadmium added to a synthetic medium showed non‐toxic, toxic, and lethal ranges of cadmium concentrations in the medium. In the non‐toxic range(less than 5 μg Cd/ml), the growth amount kept nearly constant without any alteration in cell size, while it decreased with an increased cell size in the toxic range(more than 5 μg Cd/ml). By increasing zinc concentration in medium, the effect of cadmium on the growth amount and cell size was reduced with the resulting decrease in cadmium incorporation into cells.