Sterol glycosides and cerebrosides accumulate in Pichia pastoris, Rhynchosporium secalis and other fungi under normal conditions or under heat shock and ethanol stress

The occurrence of glycolipids such as sterol glycosides, acylated sterol gl ycosides, cerebrosides and glycosyldiacylglycerols was examined in the thre e yeast species Candida albicans, Pichia pastoris is and Pichia anomala, as well as in the six fungal species Sordaria macrospora, Pyrenophora teres, Ustilago maydis, Acremonium chrysogenum, Penicillium olsonii and Rhynchospo rium secalis. Cerebroside was found in all organisms tested, whereas acylat ed sterol glycosides and glycosyldiacylglycerols were not found in any orga nism. Sterol glycosides were detected in P, pastoris strain GS115, U. maydi s, S. macrospora and R. secalis, This glycolipid occurred in both yeast and filamentous forms of U, maydis but in neither form of C, albicans. This su ggests that sterol glycoside is not correlated with the separately grown di morphic forms of these organisms. Cerebrosides and sterol glycosides from P , pastoris and R, secalis were purified and characterized by mass spectrome try and nuclear magnetic resonance spectroscopy. The cerebrosides are beta -glucosyl ceramides consisting of a saturated alpha -hydroxy or non-hydroxy fatty acid and a Delta4,8-diunsaturated, C9-methyl-branched sphingobase. S terol glycoside from P. pastoris was identified as ergosterol-P-D-glucopyra noside, whereas the sterol glucosides from R. secalis contain two derivativ es of ergosterol, The biosynthesis of sterol glucoside in P, pastoris CBS74 35 and GS115 depended on the culture conditions. The amount of sterol gluco side in cells grown in complete medium was much lower than in cells from mi nimal medium and a strong increase in the content of sterol glucoside was o bserved when cells were subjected to stress conditions such as heat shock o r increased ethanol concentrations. From these data we suggest that, in add ition to Saccharomyces cer cerevisiae, new yeast and fungal model organisms should be used to study the physiological functions of glycolipids in euka ryotic cells. This suggestion is based on the ubiquitous and frequent occur rence of cerebrosides and sterol glycosides, both of which are rarely detec ted in S, cerevisiae. We suggest P. pastoris and two plant pathogenic fungi to be selected for this approach. Copyright (C) 2001 John Wiley & Sons, Lt d.