Cong T. Trinh and Friedrich Srienc. Chem. Eng. & Matl. Sci. and BioTechnology Institute, University of Minnesota, 1479 Gortner Ave, St. Paul, MN 55108
During production of biodiesel from vegetable oils or animal fats, glycerol is produced as an unavoidable byproduct that makes up about 10% (w/w) of the total product yield. To utilize the potential surplus of this byproduct, we have developed a metabolically engineered E. coli that can efficiently convert glycerol into bioethanol. Using elementary mode analysis, we have designed a mutant E. coli that can operate only according to efficient pathways for converting glycerol into ethanol under optimal growth conditions. The mutant is also designed to tightly couple cell growth and ethanol production to facilitate metabolic pathway evolution. The operation of the designed pathways in the mutant has been enforced by implementing 9 gene knockout mutations. Characterization of the mutant in controlled bioreactors shows that the mutant is able to convert 40 g/L of glycerol into ethanol in defined medium within 48 hours and achieves at least 90% of the theoretical ethanol yield (0.5 g ethanol/g glycerol). We demonstrate that the performance of the mutant closely matches the theoretical prediction.
