Engineering the push and pull of lipid biosynthesis in oleaginous yeast Yarrowia lipolytica for biofuel production

Microbial oil production by heterotrophic organisms is a promising path for the cost-effective production of biofuels from renewable resources provided high conversion yields can be achieved. To this end, we have engineered the oleaginous yeast Yarrowia lipolytica. We first established an expression platform for high expression using an intron-containing translation elongation factor-1α (TEF) promoter and showed that this expression system is capable of increasing gene expression 17-fold over the intronless TEF promoter. We then used this platform for the overexpression of diacylglycerol acyltransferase (DGA1), the final step of the triglyceride (TAG) synthesis pathway, which yielded a 4-fold increase in lipid production over control, to a lipid content of 33.8% of dry cell weight (DCW). We also show that the overexpression of acetyl-CoA carboxylase (ACC1), the first committed step of fatty acid synthesis, increased lipid content 2-fold over control, or 17.9% lipid content. Next we combined the two genes in a tandem gene construct for the simultaneous coexpression of ACC1 and DGA1, which further increased lipid content to 41.4%, demonstrating synergistic effects of ACC1+DGA1 coexpression. The lipid production characteristics of the ACC1+DGA1 transformant were explored in a 2-L bioreactor fermentation, achieving 61.7% lipid content after 120h. The overall yield and productivity were 0.195g/g and 0.143g/L/h, respectively, while the maximum yield and productivity were 0.270g/g and 0.253g/L/h during the lipid accumulation phase of the fermentation. This work demonstrates the excellent capacity for lipid production by the oleaginous yeast Y. lipolytica and the effects of metabolic engineering of two important steps of the lipid synthesis pathway, which acts to divert flux towards the lipid synthesis and creates driving force for TAG synthesis.