(132c) Kinetic Modeling of Isobutanol Fermentation by Recombinant Escherichia Coli
This study explored the kinetics of isobutanol fermentation from an engineered E. coli strain which was constructed by introducing a kivd gene encoding 2-ketoisovalerate decarboxylase and an adhA gene encoding aldehyde reductase. Using a well-controlled bioreactor, we performed fermentation under aerobic and oxygen-limited conditions with minimal and rich media. From these experiments, four general observations emerged. 1) Isobutanol production was correlated with biomass growth, and it reached 0.95 g/L in a closed oxygen-limited bioreactor. 2) Oxygen-limited conditions generated significant amount of byproducts (lactate and ethanol); 3) Byproduct acetate reduced alcohol fermentation and biomass growth via non-competitive inhibition; 4) Nutrients enhanced biomass growth and offered building blocks for faster isobutanol production (inferred from isotopic experiments), but they also generated more byproducts and reduced the yield of isobutanol from glucose. Based on the experimental data, we then built an empirical Monod-based model that described the time-dependent bioprocess variables, including glucose consumption, biomass growth, isobutanol production, and metabolic byproduct secretion (ethanol, lactate, and acetate). Such a kinetic model can provide important knowledge underlying the design of optimal bioprocess conditions for higher alcohol production.