Metabolic engineering of Torulopsis glabrata for improved pyruvate production

During pyruvate production, ethanol is produced as a by-product, which both decreases the amount of pyruvate and makes the recovery of pyruvate more difficult. Pyruvate decarboxylase (PDC, EC 4.1.1.1), which degrades pyruvate to acetaldehyde and ultimately to ethanol, is a key enzyme in the pyruvate metabolism of yeast. Therefore, to order to increase the yield of pyruvate in Torulopsis glabrata, targeted PDC-disrupted strains were metabolically engineered. First, T. glabrata ura3 strains that were suitable for genetic transformation were isolated and identified through ethyl methansulfonate mutagenesis, 5-fluoroortic acid media selection, and Sacchramyces cerevisiae URA3 complement. Next, the PDC gene in T. glabrata was specifically disrupted through homologous recombinant with the S. cerevisiae URA3 gene as the selective marker. The PDC activity of the disruptants was about 33% that of the parent strain. Targeted PDC gene disruption in T. glabrata was also confirmed by PCR amplification and sequencing of the PDC gene and its mutants, PDC activity staining, and PDC Western blot. The disruptants displayed higher pyruvate accumulation and less ethanol production. Under basal fermentation conditions (see Section 2), the disruptants accumulated about 20 g/L of pyruvate with 4.6 g/L of ethanol, whereas the parental strain (T. glabrata IFO005) only accumulated 7–8 g/L of pyruvate with 7.4 g/L of ethanol. Under favorable conditions in jar fermentation, the disruptants accumulated 82.2 g/L of pyruvate in 52 h.