Rewiring Metabolism to Maximize Lipid Overproduction in Yarrowia lipolytica

Authors: 
Stephanopoulos, G., Massachusetts Institute of Technology
Wasylenko, T., Massachusetts Institute of Technology
Xu, P., MIT

Production of lipids by microbial fermentation of carbohydrate feedstocks outcompetes oil crops in terms of productivity, however, presently achievable carbohydrate-to-lipid process yields have not yet reached the point that can support cost-effective production of lipids and biodiesel. To improve process yields, one needs to maximize lipid content and capture as many of the electrons generated from the catabolism of substrates as possible. Guided by a quantitative model that predicts process yield, Y from the non-lipid biomass yield, lipid content, and yield of lipid synthesis pathway, we show that Y is significantly improved by introducing synthetic pathways that recycle glycolytic NADHs into cytosolic NADPH or acetyl-CoA. We experimentally built and evaluated thirteen engineered strains, with the best strain achieving a lipid titer of 99 g/L with a productivity of 1.2 g/L/h and an overall process yield 0.269 g-FAME/g-glucose. These figures of merit advance the commercialization opportunities of carbohydrate-based lipids production. In addition, these Yarrowia strains show promise in lipid production from other feedstocks, especially when integrated with fermentation of gases fixing CO2 with hydrogen or carbon hydroxide to produce volatile fatty acids. Results on an integrated system converting syngas to lipids will be presented as a model for a biological Gas-to-Liquids (GTL) process.