Cold Adaptation in a Psychrotolerant Micromycete Mucor flavus

Abstract

To study the mechanisms of protection of the cell membranes and macromolecules from cold, the composition of osmolytes, membrane lipids, and their fatty acids in a submerged culture of Mucor flavus was analyzed in growth dynamics at 20 and 4°C. This micromycete is psychrotolerant, having a wide growth temperature range (from –2 to 25°C) with an optimum at 20°C. Mucor flavus has a high growth rate (15 mm/day at 20°C, 4 mm/day at 0°C). At both temperatures, phosphatidic acids and phosphatidylethanolamines were predominant in the composition of membrane lipids, while phosphatidylcholines were the minor components. The main difference in the composition of membrane lipids was the threefold lower share of sterols at 4°C. During growth under optimal conditions, the proportion of phosphatidic acids decreased against the background of a slight increase in the levels of sterols, phosphatidylethanolamines, and phosphatidylcholines, while at 4°C the proportion of phosphatidic acids decreased slightly and the proportion of phosphatidylcholines increased. The fatty acids composition of phospholipids during growth at 20°C did not change significantly; linoleic, oleic, linolenic, and palmitic acids were predominant. At 4°C, the proportion of palmitic acid decreased and that of oleic acid increased, while the proportion of γ-linolenic acid decreased by half while that of α-linoleic acid increased. However, these changes did not lead to a significant change in the unsaturation degree of phospholipids, which varied between 1.5 and 1.6. Trehalose and glucose were the predominant osmolytes of the cytosol; glycerol was present in minor amounts only at 4°C. At both temperatures, the amount of osmolytes reached 3% of the dry weight in the course of growth, and the proportion of trehalose reached 70%. At both temperatures, a constant composition of osmolytes and slight changes in the composition of membrane lipids and their degree of unsaturation were observed, which probably contributes to the high growth rate of the fungus over a wide temperature range.