(15f) Understanding and Enhancing Bioconversion of Acetic Acid to Biodiesel Using Yarrowia lipolytica

Acetate is an inexpensive and renewable carbon source that can be generated from various sources such as pyrolysis of lignocellulosic biomass and anaerobic digestion of fermentable wastes. The oleaginous yeast Yarrowia lipolytica is a promising biocatalyst that can utilize acetate and convert it into triacylglycerides (TAGs), a precursor for green diesel. However, currently there is limited knowledge on the metabolism of Y. lipolytica when cultured on acetate. To develop a better understanding, we used sodium acetate as the sole carbon source and performed ¹³C-MFA on two different strains as well as two fermentation phases—growth (nitrogen present) and lipid production (nitrogen depleted and cells no longer synthesize biomass). The resolved flux distributions demonstrated that the glyoxylate shunt pathway is constantly active in both strains and phases. Furthermore, the cells were able to divert an adequate amount of glyoxylate shunt flux to gluconeogenesis through the PEP-pyruvate node. In this way, the oxidative pentose phosphate pathway remained active even when the cells no longer divide to generate sufficient lipogenic NADPH for TAG accumulation. Based on these conclusions, we also demonstrated that the enhancement of acetate utilization and conversion into TAGs can be achieved by providing the cells with another substrate to increase flux through upper glycolysis.