Genetic modification of industrial yeast strains to obtain controllable NewFlo flocculation property and lower diacetyl production

The expression cassette 110 containing the new-found flocculation gene, FLONS, was transformed into an industrial strain Saccharomyces cerevisiae YSF5. Upstream activating sequences of the S. cerevisiae alcohol dehydrogenase II (ADH2) gene promoter (PU-ADH2) were used to regulate the expression of FLONS; alpha-acetolactate synthase gene ILV2 was chosen for homologous recombination of 110 to the YSF5 chromosome; copper binding metallothionein (encoded by CUP1) was used for selection of transformants. Ten randomly selected transformants exhibited increased flocculation ability of 1.5 to 2.3 fold more than the original strain. Based on their sensitivity to glucose, maltose and sucrose, flocculation property of the transformants was supported to be NewFlo-type. After successive subculture, the introduced CUP1 remained in the transformants. At the end of simulated fermentation test, diacetyl content of the culture media of 5I-1 was 0.45 g l(-1), lower than YSF5 (0.48 g l(-1)).