New industrial brewing yeast strains with ILV2 disruption and LSD1 expression.

New industrial brewing yeast strains, free of vector sequences and drug-resistance genes, were constructed by disrupting alpha-acetohydroxyacid synthase (AHAS) gene (ILV2) and introducing Lipomyces starkeyi dextranase (DEX) gene (LSD1) as a selective marker. The resulting recombinant strains can survive on YNB minimal medium plate with dextran T-70 as sole carbon source and showed lower AHAS activity. Fermentation test with recombinant strains in 500 ml conical flask confirmed DEX activity and lower AHAS activity compared with their host strain. Moreover, the fermentative performance of recombinant strains T1 and Q9 was better than their host, and the residual sugar content was reduced by 20-25% in fermented wort with recombinant strains compared to their host, too.