Metabolic engineering of Saccharomyces cerevisiae for accumulating pyruvic acid

Pyruvate decarboxylase (PDC), a key enzyme in alcoholic fermentation in Saccharomyces cerevisiae, can degrade pyruvic acid to further convert acetaldehyde into ethanol. The main structural genes encoding PDC are PDC1 and PDC5. In this study, metabolic engineering principles were used to block the further metabolism of pyruvic acid; Saccharomyces cerevisiae Y2-1 with PDC1 disruption and Y2-15 with both PDC1 and PDC5 disruption were obtained using the LiAc/SS carrier DNA/PEG method. The specific PDC activity of mutant S. cerevisiae Y2-1 decreased by 31 % compared to that of the parent strain Y2, while specific PDC activity was barely detectable in mutant S. cerevisiae Y2-15. Moreover, the mutant Y2-1 with PDC1 disruption displayed no obvious effect on the rate of growth in the yeast nitrogen base with glucose (YNBG) medium, but the growth rate of S. cerevisiae Y2-15 was significantly lower than that of the parent strain Y2. Finally, through optimization of the fermentation medium, the accumulation of pyruvic acid by Y2-15 increased to 24.65 g/L over a period of 96 h, 16.86-fold higher than with the parental strain Y2 by shake flask cultivation.