(491d) Effects of Artificial Electron Carriers on Increasing NADH Availability, Acetate Re-Assimilation and Butyric Acid Production By Clostridium Tyrobutyricum

Clostridium tyrobutyricum produces butyric and acetic acids from glucose. The maximum theoretical yield and selectivity of butyric acid in the fermentation depends on the availability of NADH, which favors the more reduced product. In this study, three kinds of artificial electron carriers (benzyl viologen (BV), methyl viologen (MV) and neutral red (NR)) that inhibit hydrogen production, was used to increase NADH availability and butyric acid production while simultaneously eliminate the accumulation of by-product, acetic acid by facilitating its re-assimilation. In order to understand the mechanism and find the optimum condition contributing to artificial electron carriers function efficiently, the effects of BV, MV and NR at various concentrations, and their addion time on butyric acid production were studied. Compared with the control (C. tyrobutyricum mutant strain HydEm), the addition of BV increased butyric acid final concentration by 10%, yield by 32% and productivity by 6% in the feb-batch fermentation using bioreactor with accurate pH control. Most importantly, acetate was completely re-assimilated and 99% purity of butyric acid was obtained, which would greatly decrease the recovery cost and increase economic feasibility of bio-based butyric acid production. The result demonstrates that redox equilibrium can be exploited to drive carbon flux redistribution for desirable metabolic product.