Effect ofhxk2deletion andHAP4overexpression on fermentative capacity inSaccharomyces cerevisiae

To describe the fermentative potential of a yeast cell, the fermentative capacity (FC) has been defined as the specific rate of ethanol and CO2 production under anaerobic conditions. The effect of growth rate on FC of glucose-limited grown Saccharomyces cerevisiae strains with altered expression of two major glycolytic regulators, Hap4p and Hxk2p, was compared with their parent strain. Whereas overproduction of Hap4p behaved similar to the wild-type strain, deletion of hxk2 resulted in a very different FC profile. Most importantly, with maltose as the carbon and energy source, the latter strain expressed an FC twofold that of the wild type. Further analysis at the level of gene expression showed large changes in ADH2 transcripts and to a lesser extent in hexose transporters and genes involved in the glyoxylate cycle. With respect to primary glucose metabolism, a shift in the type of hexose transport to one with high affinity was induced. In accordance with the phenotype of the mutant strain, the maltose transporter was constitutively expressed under glucose-limited conditions and synthesis increased in the presence of maltose.