Effect of zinc on the yeast-mycelium transition of Candida albicans and examination of zinc uptake at different stages of growth

Effects of Zn2+ on dimorphism in Candida albicans 3153A were dependent on the external Zn2+ concentration and the temperature of incubation. Micromolar Zn2+ concentrations suppressed the yeast-mycelium transition at 25 °C, whereas at 30° and 37° germ-tube development was possible at millimolar Zn2+ concentrations. Both yeast cells and germ-tubes exhibited energy-dependent Zn2+ uptake, which was dependent on the electrochemical proton gradient across the cell membrane. However, germ-tubes accumulated much greater amounts of Zn2+ than yeast cells under similar conditions. The higher Zn2+ uptake by germ-tubes at 10 m-ZnCl2, in comparison with yeast cells, was the probable cause of inhibition of germ-tube formation at 25°. In both cell types, Zn2+ uptake was concentration-dependent and subject to pH and temperature control. At a low Zn2+ concentration (10 m), uptake in either cell type was markedly greater at 25° than at 30° and 37°, whereas at 100 m-Zn2+ uptake was greatest at 37° and 30° and lowest at 25°. These differing characteristics of Zn2+ uptake, including temperature responses, resulted from the nature of the Zn2+ transport systems possessed by C. albicans. Kinetic analysis showed the existence of more than one transport system at 37° and Zn2+ uptake by yeast cells and germ-tubes only conformed to saturation kinetics below approximately 50 m-Zn2+. Values of the Km and Vmax for yeast cells over this concentration range were 2·2 m and 0·004 nmol min−1 (107 cells)−1 respectively; corresponding values for germ-tubes were 29 m and 0·04 nmol min−1 (107 cells)−1. Zn2+ transport in both cell types was reduced with decreasing external pH and inhibited by other divalent cations, particularly Ca2+ ; the extent of such inhibition varied depending on the Zn2+ concentration and cell type ex</p