Roles of Ca2+ in hyphal and yeast-form growth in Candida albicans. Growth regulation by altered extracellular and intracellular free Ca2+ concentrations

Abstract

The dimorphic fungusCandida albicans has both a yeast form and a hyphal form. When yeast-form cells were starved and then transferred to aN-acetylglucosamine medium, the formation of true hyphae from the unbudded yeast-form cells was induced. Removal of Ca2+ from the medium with EGTA inhibited hyphal formation by 50%, resulting in only thin and short hyphae. Externally applied excess Ca2+ (>10−2M) also affected the hyphal formation, resulting in formation of pseudohyphae. This effect required a high concentration of Ca2+ but was Ca2+-specific. Deprivation of Ca2+ also inhibited yeast-form growth. Interestingly, such cells had abnormally wide bud necks and became defective in cell separation. To measure cytosolic free Ca2+, fura-2 was introduced into hyphal cells by electroporation. Its normal value was estimated to be about 100 nM. The electroporation caused transient elevation of cytosolic free Ca2+ concentration and transient cessation of hyphal growth. There was a close correlation between the timing of recovery of Ca2+ concentration and that of the resumption of hyphal growth. Our results demonstrate the importance of extracellular and intracellular free Ca2+ for the growth ofC. albicans.