The involvement of cell wall expansion in the two modes of mycelium formation of Candida albicans.

When budding cells of Candida albicans are starved for 20 min and then diluted into fresh nutrient medium at 37 degrees C, pH 6.7, they form mycelia by two alternative modes. For cells with small buds, the bud expands apically, resulting in a transiently tapered daughter cell. With continued growth, the daughter cell tapers into an elongated mycelium. For cells with large buds, the bud completes expansion in the budding form, the mother cell and then the daughter bud evaginate, and the evaginations grow as mycelia. The present study investigates whether the temporal and spatial changes in the zones of wall expansion during bud growth are involved in the two modes of mycelium formation. Data are presented which demonstrate that the transition circumference which determines the two modes of mycelium formation and the transition circumference at which the active apical expansion zone shuts down are both 7 micron. This exact correlation suggests that starved cells with buds with a circumference of less than 7 micron form mycelia in the tapering mode due to the reactivation of the still present apical expansion zone, and that starved cells with buds with a circumference greater than 7 micron complete bud growth by general expansion due to the absence of the apical expansion zone at the time of starvation.