Inhibition of the differentiation of Candida albicans by the chelator 1,10-phenanthroline

Several chelators were examined for their ability to prevent the synchronous release of 24- to 48-hour stationary phase singlet cells of the dimorphic yeast Candida albicans into either the mycelial or the budding phenotypes (in a defined liquid medium at 37°C; at pH 6.5 or pH 4.5, respectively). The only chelator that was found to inhibit mycelium formation completely and to restrict bud formation to about 10% was 1,10-phenanthroline at minimal concentrations of 50 M and 230 M, respectively.The inhibition of both phenotypes could be reversed completely by the addition of 200 M of ZnSO₄. The synchrony of recovery from inhibition by the addition of zinc paralleled that of the controls for both phenotypes, and the final number of mycelia or buds as a percentage of the control was the same (100%).These findings support the hypothesis that the lag period between the release from stationary phase and the onset of development for Candida represents the time of acquisition of a minimum threshold amount of a cation, such as zinc. The involvement of zinc in phenotypic development is discussed, suggesting that while zinc is involved in the initiation of development, it may not determine the phenotype of Candida albicans.