This study examined the morphological and chemical changes in Pullularia pullulans as it transitions from yeast-like cells to chlamydospores when grown on unbuffered glucose medium with limiting nitrogen. Researchers tracked growth kinetics, cell morphology, and biochemical composition over 14 days. Yeast-like cells progressively enlarged and eventually produced chlamydospores, accompanied by marked increases in carbohydrate content and decreases in proteins and nucleic acids. The study revealed significant changes in phospholipid composition, with major variations between days 10-14 when chlamydospores formed most abundantly. Fatty acid unsaturation decreased rapidly during exponential growth and continued declining throughout the experiment. Enzymatic analysis of cell walls showed increasing glucanase sensitivity with age, indicating structural changes. Notably, protoplasts could only be prepared from 1-day-old yeast-like cells; older cells were too mechanically fragile. The results demonstrate that nutritional control, particularly nitrogen limitation, induces this morphogenetic transition and triggers coordinated changes in cell wall composition, lipid metabolism, and overall cellular chemistry as the fungus transforms into a stress-resistant form.

Key findings

• Nitrogen limitation on unbuffered glucose medium induces transition from yeast-like cells to chlamydospores in P. pullulans over 14 days
• Carbohydrate content increases while proteins and nucleic acids decrease during morphogenesis, indicating transformation into a resistant form
• Phospholipid composition undergoes substantial changes, particularly between days 10-14 during maximum chlamydospore formation
• Cell wall structure changes with age, showing increasing susceptibility to glucanase digestion in older cells
• Protoplasts can only be successfully prepared from 1-day-old yeast-like cells; older cell forms lack viable protoplasts