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

According to its growth rate at different temperatures, the ascomycete Leuconeurospora pulcherrima is a psychrophile, since it grows in a temperature range from –2 to 22.5°C, with optimum growth at 15°C. To study the mechanisms of adaptation to cold, the fungus was grown in a submerged culture at optimal (15°C) and lowered (5°C) temperatures. The amount of osmolytes reached 10% at 15°C, and in cold conditions it was twice as low. Trehalose (60% of the total) and a polyol mannitol (30%) dominated among the fungal osmolytes at the optimal temperature, and their ratio did not change during growth. At 5°C, their ratio also did not change during growth, but the proportion of mannitol increased slightly (35%) and the proportion of trehalose decreased (55%). The membrane lipid profile at both temperatures was dominated by phosphatidylethanolamines, phosphatidic acids, and phosphatidylcholines. At 15°C, the proportions of the main phospholipids did not change during growth, although the share of sterols doubled. On the contrary, during growth at 5°C, a significant increase in the shares of phosphatidylethanolamines and phosphatidylcholines was observed against the background of a decrease in the proportion of phosphatidic acids, while the proportion of sterols remained constantly low. Under optimal conditions, linoleic acid dominated in the composition of fatty acids of phospholipids (60% of the total), and at 5°C, linoleic and linolenic acids predominated, which resulted in a significant increase in the degree of unsaturation (up to 2.0). Thus, to adapt to cold, the fungus regulated the membrane fluidity by significantly increasing the relative content of linolenic acid in phospholipids, decreasing the sterol/phospholipid ratio, predominance of non-bilayer lipids in membranes, and increasing the mannitol/trehalose ratio.