MITOCHONDRIAL-DNA LOSS CAUSED BY ETHANOL IN SACCHAROMYCES FLOR YEASTS

Saccharomyces flor yeasts proliferate at the surface of sherry wine, w hich contains over 15% (vol) ethanol, Since ethanol is a powerful indu cer of respiration-deficient mutants, this alcohol has been proposed t o be the source of the high diversity found in the mitochondrial genom es of flor yeasts and other,vine yeasts. Southern blot analysis sugges ts that mitochondrial DNA (mtDNA) polymorphic changes are due to minor lesions in the mitochondrial genome, As determined in this work by pu lsed-field gel electrophoresis, restriction analysis, and Southern blo t analysis, ethanol-induced petite mutants completely lack mtDNA (rho( 0)). Ethanol-induced changes in the mitochondrial genome that could ex plain the observed mtDNA polymorphism in flor yeasts were not found. T he transfer of two different mtDNA variants from flor yeasts to a labo ratory strain conferred in both cases an increase in ethanol tolerance in the recipient strain, suggesting that mtDNAs are probably subjecte d to positive selection pressure concerning their ability to confer et hanol tolerance.