Expression of GAI gene and disruption of PEP4 gene in an industrial brewer's yeast strain.

AIMS Construction of an industrial brewer's yeast strain, which could improve foam stability and reduce calorific values of beer. METHODS AND RESULTS An industrial brewer's yeast strain (Ts-10) was constructed by integrating glucoamylase encoding gene GAI amplified from Saccharomycopsis fibuligera by PCR into the locus of proteinase A (PrA) gene (PEP4). The resulting recombinant strain identified by PCR could grow on YNB minimal medium plate with starch as sole carbon source. Its highest GAI activity was 91.69 U ml(-1), but it had no PrA activity. The real extract was reduced by 21.07% and the main residual maltotriose content was reduced by 14% in wort fermented with the recombinants strain. Its foam retention in beer was higher 39 s and the contents of potential off-flavour compounds, such as diacetyl, pentanedione and acetaldehyde were lowered by 16%, 13% and 14%, respectively, as compared with the industrial brewer's yeast YSF-5. CONCLUSIONS An industrial brewer's yeast strain was constructed by introducing GAI gene and disrupting PEP4 gene. SIGNIFICANCE AND IMPACT OF THE STUDY The recombinant strain (Ts-10) had better foam performance and mouthfeel in addition to low-calories values. It was free of heterologous DNA sequences and drug-resistance genes and could be safely used in beer production.