Adaptation of the Acidophilic Fungus Sistotrema brinkmannii to the pH Factor

Abstract—: Investigation of the growth rate of Sistotrema brinkmannii at different pH values, temperature, and NaCl concentration showed that this fungus was a mesophile, preferred a salt-free medium, and was an obligate acidophile, since it had a pronounced growth optimum at pH 3.0–4.0 and did not grow at pH 7.0. To reveal the protective mechanisms allowing this fungus to develop under acidic conditions, the composition of its osmolytes and lipids was studied. This is the first report on occurrence of a large amount of trehalose (4.0‒6.6% of dry weight) in the mycelium of the fungus during its growth under optimal conditions, confirming the use of osmolytes by acidophiles for adaptation. At the same time, at the borders of the growth range (pH 2.6 and 6.0), the amount of trehalose in the mycelium of the fungus decreased by 2.5 times, which was in agreement with a narrow growth optimum of the fungus in its natural environments (pH 3.0–4.0). The composition of membrane lipids of the fungus was characterized by a high proportion of sphingolipids (up to 60% of the total), which decreased twofold during growth under optimal conditions. The main membrane lipids, apart from sphingolipids, were phosphatidic acids, phosphatidylethanolamines, and sterols; the proportion of these lipids increased with time. The composition of membrane lipids of the fungus at pH 2.6 did not differ much from the optimal conditions, while in the near-neutral region there was a twofold increase in the proportion of sphingolipids, indicating their adaptive value. The simultaneous decrease in the proportion of sphingolipids and the increase in the level of trehalose in the growth dynamics suggest association of these compounds in the protection of cell membranes.