Overexpression of the glucoamylase-encoding STA1 gene of Saccharomyces cerevisiae var. diastaticus in laboratory and industrial strains of Saccharomyces

Production of glucoamylase encoded by the Saccharomyces cerevisiae (var. diastaticus) STA1 gene has been assayed in laboratory S. cerevisiae strains of different ploidy and in different industrial Saccharomyces strains, in which STA1 was expressed under control of an inducible promoter. Highest enzyme activity was achieved with a tetraploid strain constructed by crossing preselected parental strains. Maximal glucoamylase production correlated with heterogeneity in enzyme mass, likely due to incomplete glycosylation, suggesting that the secretion-glycosylation process is the limiting step in the production of the STA-encoded glucoamylase by Saccharomyces. Industrial strains showed quite different capacity to produce glucoamylase. High production was achieved with a S. pastorianus brewer's strain. Overall, our results allowed the selection of strains capable of yielding a high level of glucoamylase and suggest specific approaches for further enhancing this capability.