Growth and the inducibility of mycelium formation in Candida albicans: a single-cell analysis using a perfusion...

In Candida albicans, cells actively growing in the budding form cannot be immediately induced to form a mycelium until they enter stationary phase. However, if exponential phase cells are starved for a minimum of 10 to 20 min, they are inducible. Using a video-monitored perfusion chamber, we found that starved cells were able to form mycelia regardless of their position in the budding cycle. When starved exponential cells were released into fresh nutrient medium at high temperature and pH, conditions conducive to mycelium formation, unbudded cells evaginated after an average lag period of 75 min and then grew exclusively in the mycelial form. Depending upon the volume, or maturity, of the bud, budded cells entered two different avenues of outgrowth leading to mycelium formation. If the daughter bud was small, growth resumed by apical elongation of the bud, leading to a 'shmoo' shape which tapered into an apical mycelium. If the daughter bud was large, the cell underwent a sequence of evaginations: first, the mother cell evaginated after an average period of 75 min; then the daughter bud evaginated 40 min later. Both evaginations then grew in the mycelial form. In this latter sequence, the evagination on the mother cell was positioned non-randomly, occurring in the majority of cells adjacent to the bud. All buds undergoing evagination contained a nucleus, but roughly 20% of buds undergoing apical elongation did not.