Differences in membrane order parameter and antibiotic sensitivity in ergosterol-producing strains of Saccharomyces cerevisiae

Abstract

Gas chromatography of free sterols derived from exponential cultures of Saccharomyces cerevisiae strains which produce varying amounts of ergosterol indicated the presence of a previously unreported sterol peak. Gas chromatographic/mass spectral analyses of the composition of this peak have identified ergosta-5,7-dien-3β-ol, ergosta-7,22-dien-3β-ol and an unidentified sterol, molecular weight m/z 400, as peak components in wild-type strains. Analysis of strain nyr5, an ergosterol-producing slightly nystatin-resistant variant, showed this strain to be a leaky mutant of the 22(23) desaturase in the ergosterol biosynthetic pathway. Electron paramagnetic resonance (EPR) studies of membrane fluidity indicated that increased ergosterol levels resulted in higher order parameters when 5-doxyl stearic acid was employed as a membrane probe. There was no order parameter change with 7-doxyl stearic acid which seems to indicate a specificity of location in sterol packaging into the membrane. Yeast strains can be distinguished from each other based on the level of ergosterol produced by their sensitivity to the polyene antibiotic, nystatin.