Ethanol-Induced Leakage in Saccharomyces cerevisiae : Kinetics and Relationship to Yeast Ethanol Tolerance and Alcohol Fermentation Productivity

Abstract

Ethanol stimulated the leakage of amino acids and 260-nm-light-absorbing compounds from cells of Saccharomyces cerevisiae . The efflux followed first-order kinetics over an initial period. In the presence of lethal concentrations of ethanol, the efflux rates at 30 and 36°C were an exponential function of ethanol concentration: k e X = k e Xm e E (X-X m ) , where k e X and k e Xm are the efflux rate constants, respectively, in the presence of a concentration X of ethanol or the minimal concentration of ethanol, X m , above which the equation was applicable, coincident with the minimal lethal concentration of ethanol. E is the enhancement constant. At 36°C, as compared with the corresponding values at 30°C, the efflux rates were higher and the minimal concentration of ethanol ( X m ) was lower. The exponential constants for the enhancement of the rate of leakage ( E ) had similar values at 30 or 36°C and were of the same order of magnitude as the corresponding exponential constants for ethanol-induced death. Under isothermic conditions (30°C) and up to 22% (vol/vol) ethanol, the resistance to ethanol-induced leakage of 260-nm-light-absorbing compounds was found to be closely related with the ethanol tolerance of three strains of yeasts, Kluyveromyces marxianus, Saccharomyces cerevisiae , and Saccharomyces bayanus . The resistance to ethanol-induced leakage indicates the possible adoption of the present method for the rapid screening of ethanol-tolerant strains. The addition to a fermentation medium of the intracellular material obtained by ethanol permeabilization of yeast cells led to improvements in alcohol fermentation by S. cerevisiae and S. bayanus . The action of the intracellular material, by improving yeast ethanol tolerance, and the advantages of partially recycling the fermented medium after distillation were discussed.