Integrative Expression of Glucoamylase Gene in a Brewer’s Yeast Saccharomyces pastorianus Strain

The recombinant brewer’s yeast Saccharomyces pastorianus strain was constructed by introducing the ilv2::GLA fragment released from pMGI6, carrying glucoamylase gene (GLA) and using the yeast a-acetolactate synthase gene (ILV2) as the recombination sequence. The strain was able to utilise starch as the sole carbon source, its glucoamylase activity was 6.3 U/mL and its a-acetolactate synthase activity was lowered by 33.3 %. The introduced GLA gene was integrated at the recipient genomic ILV2 gene, one copy of ILV2 gene was disrupted and the other copy remained intact. Primary wort fermentation test confirmed that the diacetyl and residual sugar concentration in the wort fermented by the recombinant strain were reduced by 65.6 and 34.2 % respectively, compared to that of the recipient strain. Under industrial operating conditions, the maturation time of beer fermented by the recombinant strain was reduced from 7 to 4 days, there were no significant differences in the appearance and mouthfeel, and the beer satisfied the high quality demands. That is why the strain could be used in beer production safely.