Metabolic Engineering of Saccharomyces Cerevisiae for the Overproduction of Short Branched-Chain Fatty Acids

Short branched-chain fatty acids (sBCFAs, C4-6) are versatile platform chemicals in high demands because they can be converted to a wide range of valuable products in the manufacturing, pharmaceutical and food industry. For example, their esters are used for the production of plastics, plasticizers, surfactants, textile auxiliaries, fragrances and flavorings. Currently, sBCFAs are mainly synthesized chemically, which can be costly and causes pollution. In order to develop a more economical and environmentally friendly route for sBCFAs production, we engineered Saccharomyces cerevisiae, a model eukaryote of industrial significance, for the overproduction of sBCFAs. S. cerevisiae natively produces the sBCFAs isobutyric acid, isovaleric acid, and 2-methylbutyric acid from branched-chain amino acids via the Ehrlich pathway. However, the natural production levels of these sBCFAs are very low in S. cerevisiae. In order to utilize S. cerevisiae as an efficient cell factory for high-level production of our target sBCFAs, we optimized the endogenous Ehrlich pathway for sBCFA biosynthesis. We achieved overproduction of sBCFA in yeast by overexpressing pathway genes, knocking out genes in competitive pathways, reengineering native transporters and optimizing growth conditions. Our engineered yeast can thus serve as a platform strain for biosynthesis of valuable sBCFA-derived chemicals.