Lipid composition and the transition from yeast-like to chlamydospore cells of Pullularia pullulans

The lipid composition of the fungus Pullularia pullulans has been investigated at different stages of the morphogenetic transition from yeast-like, through the so-called "large cells," to chlamydospores. The first 3 days of culture correspond to the period of exponential growth. There is a rapid consumption of glucose and ammonium, until the latter becomes exhausted, and a concomitant decrease of pH down to values of about 2. A decrease in fatty acid unsaturation takes place at this stage, together with an increase in the proportion of long-chain aldehydes. The period between days 3 and 6 is dominated by the large cells. They accumulate large amounts of triacylglycerols; phospholipids and free sterols are also synthesized in this period, suggesting de novo synthesis of membranes. Chlamydospores can be seen from the 6th day on. Simultaneously, a decrease in free sterols and phospholipids takes place, while saturated triacyglycerol production goes on. The lipid composition of chlamydospores suggests that these are resistance forms, induced by the hostile environmental conditions of the medium after the end of the exponential growth.