Ethanol tolerance and membrane fatty acid adaptation in adh multiple and null mutants of Kluyveromyces lactis

The effects of ethanol and 1-octanol on growth and fatty acid composition o f different strains of Kluyveromyces lactis containing a mutation in the fo ur different alcohol dehydrogenase (KlADH) genes were investigated. In the presence of ethanol and 1-octanol K. lactis reduced the fluidity of its lip ids by decreasing the unsaturation index (UI) of its membrane fatty acids. In this way, a direct correlation between nonlethal ethanol concentrations and the decrease in the UI could be observed. At concentrations which total ly inhibited cell growth no reaction occurred. These adaptive modifications of the fatty acid pattern of K. lactis to ethanol contrasted with those re ported for Saccharomyces cerevisiae and Schizosaccharomyces pombe. Whereas these two yeasts increased the fluidity of their membrane lipids in the pre sence of ethanol, K. lactis reduced the fluidity (UI) of its lipids. Among the different isogenic adh negative strains tested, the strain containing n o ADH (adh(0)) and that containing only KlADH1 were the most alcohol-sensit ive. The strain with only KlADH2 showed nearly the same tolerance as refere nce strain CBS 2359/152 containing all four ADH genes. This suggests that t he KlADH2 product could play an important role in the adaptation/detoxifica tion reactions of K. lactis to high ethanol concentrations. (C) 2000 Editio ns scientifiques et medicales Elsevier SAS.