Engineering oxidative stress defense pathways to build a robust lipid production platform in Yarrowia lipolytica.

Microbially derived lipids have recently attracted renewed interests due to their broad applications in production of green diesels, cosmetic additives, and oleochemicals. Metabolic engineering efforts have targeted a large portfolio of biosynthetic pathways to efficiently convert sugar to lipids in oleaginous yeast. In the engineered overproducing strains, endogenous cell metabolism typically generates harmful electrophilic molecules that compromise cell fitness and productivity. Lipids, particularly unsaturated fatty acids, are highly susceptible to oxygen radical attack and the resulting oxidative species are detrimental to cell metabolism and limit lipid productivity. In this study, we investigated cellular oxidative stress defense pathways in Yarrowia lipolytica to further improve the lipid titer, yield, and productivity. Specifically, we determined that coupling glutathione disulfide reductase and glucose-6-phosphate dehydrogenase along with aldehyde dehydrogenase are efficient solutions to combat reactive oxygen and aldehyde stress in Y. lipolytica. With the reported engineering strategies, we were able to synchronize cell growth and lipid production, improve cell fitness and morphology, and achieved industrially-relevant level of lipid titer (72.7 g/L), oil content (81.4%) and productivity (0.97 g/L/h) in controlled bench-top bioreactors. The strategies reported here represent viable steps in the development of sustainable biorefinery platforms that potentially upgrade low value carbons to high value oleochemicals and biofuels. Biotechnol. Bioeng. 2017;114: 1521-1530.