Inhibition effect of initial Pb2+ concentration on Pb2+ accumulation by Saccharomyces cerevisiae and Aureobasidium pullulans

Pb2+ accumulation by Saccharomyces cerevisiae and Aureobasidium pullulans was inhibited by the initial Pb2+ concentration. In the case of S. cerevisiae, as initial Pb2+ concentrations increased, the accumulated Pb2+ per unit cell dry weight at equilibrium and the time required to reach an equilibrium state increased at low initial Pb2+ concentration. On the contrary, the accumulated Pb2+ decreased at high initial Pb2+ concentration at all pH values. The inhibition effect of initial Pb2+ concentration was delayed by the decrease of pH. However, the maximal Pb2+ accumulation capacity of S. cerevisiae was almost constant regardless of pH values. In the case of A. pullulans, the time required to reach an equilibrium state was independent of the initial Pb2+ concentration. The maximal Pb2+ accumulation capacity of A. pullulans decreased according to the decrease of pH values. However, the initial Pb2+ concentration needed to reach maximal Pb2+ accumulation amount was almost constant.