Modulating betulinic acid production in Saccharomyces cerevisiae by managing the intracellular supplies of the co-factor NADPH and oxygen.

Betulinic acid is a plant derived triterpenoid with beneficial effects for anti-tumor and anti-human immunodeficiency virus treatments. In Saccharomyces cerevisiae, we previously constructed the betulinic acid biosynthetic pathway, in which several enzymes function in a NADPH or oxygen-dependent manner. To seek whether the intracellular supply of the NADPH/oxygen of S. cerevisiae could be managed for improving betulinic acid production, the expressions of the mutated 2,3-butanediol dehydrogenase (mBDH1) and the yeast codon optimized Vitreoscilla hemoglobin (mvhb) were separately introduced into the betulinic acid forming yeast strain. The effect of these expressions on betulinic acid productivity was evaluated. Our results showed that the expression of mBDH1 and mvhb increased the concentration of betulinic acid to 1.5 and 3.2 times, respectively relative to the controls. Meanwhile, the growth property of these engineered yeast strains was also monitored. Though the mvhb expression greatly improved the production of betulinic acid but exerted a serious inhibition on yeast growth. However, it was possible to keep desirable yeast growth phenotype using an appropriate concentration of acetoin with the expression of mBDH1. The results of this study would provide a general reference to modulate the production of other triterpenoids in S. cerevisiae by managing the supplies of NADPH and oxygen.