The Role of Osmolytes and Membrane Lipids in Cold Adaptation in the Psychrophilic Ascomycete Leuconeurospora pulcherrima

According to the growth rate at different temperatures the ascomycete Leuconeurospora pulcherrima is a psychrophile, as it grows in a temperature range from ‒2 to 22.5°C, with optimum growth observed at 15°C. To study the mechanisms of adaptation to cold, the fungus was grown in a submerged culture at optimal (15°C) and reduced (5°C) temperatures. The amount of osmolytes at 15°C reaches 10%, and in cold conditions it is twice as low. Trehalose (60% of the total) and polyol mannitol (30%) dominate in the fungal osmolytes at the optimal temperature, and their ratio does not change during growth. At 5°C, their ratio also does not change during growth, but the proportion of mannitol increases slightly (35%) and the proportion of trehalose decreases (55%). The membrane lipid profile at both temperatures is dominated by phosphatidylethanolamines, phosphatidic acids and phosphatidylcholines. At 15°C, the proportions of the main phospholipids do not change during growth, only the proportion of sterols doubles. On the contrary, at 5°C during growth, a significant increase in the proportion of phosphatidylethanolamines and phosphatidylcholines is observed against the background of a decrease in the proportion of phosphatidic acids, while the proportion of sterols remains constantly low. Under optimal conditions, linoleic acid dominates in the composition of fatty acids of phospholipids (60% of the total), and at 5°C – linoleic and linolenic, which leads to a significant increase in the degree of unsaturation. Thus, to adapt to cold, the fungus regulates membrane fluidity by significantly increasing the relative content of linolenic acid in phospholipids, decreasing the sterol/phospholipid ratio, dominating non-bilayer lipids in membranes, and increasing the mannitol/trehalose ratio.