Zinc and the regulation of growth and phenotype in the infectious yeast Candida albicans

Abstract

When Candida albicans is grown at 25°C in suspension in defined medium, cells accumulate at stationary phase as singlets in G1 of the deoxyribonucleic acid replication cycle and acquire the capacity to form mycelia. When cells were removed from a stationary-phase culture and a low concentration of fresh cells was inoculated into the cell-free, stationary-phase medium, the fresh cells grew to approximately the same cell density as the original culture. We demonstrated that in the original culture, cells do not enter stationary phase due to an accompanying decrease in pH, nor due to a depletion of O2, an accumulation of CO2, a physical crowding effect, or accumulation of the putative autoinhibitors tryptophol and 2-phenylethyl alcohol. Rather, cells stop multiplying at stationary phase due to the depletion of zinc from the culture medium. The manipulation of cultures with glassware to remove stationary-phase cells and to add fresh cells led to the addition of zinc to the medium and hence a new round of culture growth. The same manipulations with plasticware did not result in zinc supplementation and hence in no new round of culture growth. When cells enter stationary phase in excess zinc, they do not accumulate as singlets; rather, they accumulate as budded cells. When these cells were induced to form mycelia, they did so in half the time it took zinc-starved cells. The usefulness of employing zinc starvation as a method for obtaining a uniform stationary-phase phenotype and for synchronizing induced mycelium or bud formation is discussed.