Expression Patterns of Genes and Enzymes Involved in Sugar Catabolism in IndustrialSaccharomyces cerevisiaeStrains Displaying Novel Fermentation Characteristics

The utilisation of maltose or sucrose by a selection of nine brewing, baking or laboratory strains of Saccharomyces cerevisiae was either repressible, constitutive or absent. Overall fermentation rate showed a good correlation with maximum specific maltose transport rate (R2 = 0.79), but a poor correlation with maximum maltase activity (R2 = 0.34), implying that transport rather than hydrolysis of maltose was a rate-limiting step determining fermentation performance. The genetic basis for differences seen between the strains in terms of fermentation kinetics was investigated. All strains were found to possess genomic sequences detectable with probes for the MAL11 (AGT1), MAL31 permease genes and the SUC2 invertase gene, however, the loci present and the pattern of expression of these and other MAL genes varied widely. From comparisons of sugar utilisation and gene expression patterns, constitutive maltose utilisation in strain NCYC 1681 was best explained by AGT1 expression. Such expression of AGT1 was not, however, mirrored by changes in the pattern of expression of the transcriptional activator(s) (MALx3). Patterns of sucrose utilisation were poorly predicted by the kinetics of SUC2 gene expression, indicating that other SUC loci may be of greater importance.