Mutational analysis of malate pathways in Schizosaccharomyces pombe

Schizosaccharomyces pombe is of interest to wine-makers because, unlike the Saccharomyces cerevisiae wine yeasts, it eciently metabolizes all levels of malic acid found in grape musts. To determine the metabolic pathway for malatemetabolism in Sch. pombe, a mutational analysis was performed using a selection system which isolated 154mutants that were unable to utilize malic acid. Themutants were in three complementation groups which corresponded to alleles and activities for malate dehydrogenase, malic enzyme and malate transport respectively. Under anaerobic conditions Sch. pombe ferments malic acid by using a malate transport, malic enzyme, pyruvate decarboxylase, alcohol dehydrogenase pathway (a malo-ethanolic fermentation) but under aerobic conditions malate is both fermented to ethanol and to a much lesser extent, respired as a TCA cycle intermediate. Alleles were mapped genetically and the locations were con®rmed by chromoblotting. Malic enzyme and malate transport alleles were cloned by complementation and the proteins have been puri®ed and partially characterized.# 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved