Alkaliphily, the ability of an organism to thrive optimally at high ambient pH, has been well-documented in several lineages: archaea, bacteria and fungi. The molecular mechanics of such adaptation has been extensively addressed in alkaliphilic bacteria and alkalitolerant fungi. In this study, we consider an additional property that may have enabled fungi to prosper at alkaline pH: altered contents of membrane lipids and cytoprotectant molecules. In the alkaliphilic Sodiomyces tronii, we showed that at its optimal growth pH 9.2, the fungus accumulates abundant cytosolic trehalose (4-10% dry weight) and phosphatidic acids in the membrane lipids, properties not normally observed in neutrophilic species. At a very high pH 10.2, the major carbohydrate, glucose, was rapidly substituted by mannitol and arabitol. Conversely, lowering the pH to 5.4-7.0 had major implications both on the content of carbohydrates and membrane lipids. It was shown that trehalose dominated at pH 5.4. Fractions of sphingolipids and sterols of plasma membranes rapidly elevated possibly indicating the formation of membrane structures called rafts. Overall, our results reveals complex dynamics of the contents of membrane lipids and cytoplasmic sugars in alkaliphilic S. tronii, suggesting their adaptive functionality against pH stress.
Keywords: Alkaliphilic fungi; Mannitol; Membrane lipids; Sodiomyces tronii; Soluble carbohydrates; Trehalose.