Copper uptake by yeast-like cells, hyphae, and chlamydospores of Aureobasidium pullulans

All cell types of Aureobasidium pullulans could bind copper to surfaces, the efficiency of binding being in the order chlamydospores >yeast-like cells >mycelium. Chlamydospores were the least sensitive cell type to copper and only yeast-like cells and mycelium exhibited a second phase of energy-dependent Cu²⁺ influx at nontoxic concentrations. This followed Michaelis-Menten kinetics and was inhibited at 4°C or in the presence of 2-deoxy-d-glucose, potassium cyanide, high Ca²⁺ concentrations, and the uncouplers carbonylcyanide-p-trifluoromethoxyphenylhydrazone and dinitrophenol, but was stimulated by nigericin. Concomitant with Cu²⁺ influx was K⁺ efflux, and two K⁺ ions were released for every Cu²⁺ taken up. Cu²⁺ influx was inhibited when intracellular K⁺ was low or when extracellular K⁺ was high. The results suggested that Cu²⁺ influx was driven by the membrane potential. There was Cu²⁺ efflux from loaded cells which was independent of the presence of glucose, and kinetic analysis showed that the cells acted as two-compartment systems. Most of the intracellular copper could be removed by washing the cells with nitrilotriacetic acid.