Metabolic Flux Analysis Of Actinobacillus Succinogenes In Succinic Acid Fermentation

Succinic acid is a C4-dicarboxylic acid in the metabolic pathway of several anaerobic and facultative microorganisms. In order to improve the succinic acid productivity by Actinobacillus succinogenes CGMCC1593 in anaerobic fermentation, Metabolic carbon flux analysis was used to evaluate the effects of oxidation-reduction potentialcultue, nutrition factors and different pH-control methods on cell growth and the changing distributions of carbon flux fraction.In chapter two, to investigate the global metabolism of Actinobacillus succinogenes under anaerobic conditions from 50g/L of glucose, a metabolic pathways contains 20 reactions and 20 compounds was constructed up, a 20×15 matrix created by MFA was calculated by MATLAB 7.0 software. The result showed that: fraction of carbon flux at succinic acid was low whereas biomass was high during logarithmic cell growth (8h) stage; on the contrary, succinic acid flux increased 45% during metabolic stabilization (20h) stage, biomass flux decreased 80%, respectively.The topic of chapter three is the effect of ORP on cell growth and production of Actinobacillus succinogenes CGMCC1593 anaerobic fermentation. It was indicated that: the cells grew faster at a ORP of -220 mV whereas the succinic acid yield was greater at a ORP of -270 mV. MFA was used to evaluate the effects of two ORP (-220 mV, -270 mV) on the changing distributions of carbon flux fraction at the phosphoenolpyruvate (PEP) node, and pyruvate (PYR) nodes and flux distribution of NADH, during the logarithmic cell growth (8h) and metabolic stabilization(20h) stages of the batch fermentation of A. succinogenes CGMCC1593. It was shown that fraction of carbon flux at NADH and succinic acid increased significantly at ORP of -270 mV.In chapter four, distributions of carbon flux fraction in 32h-anaerobic fermentation with different pH-control methods(MgCO₃, Na₂CO₃) was calculated, flux of key nodes such as phosphoenolpyruvate (PEP) node and pyruvate (PYR) node was also investigated. The results showed that: NADH and succinic acid flux was higher under Na₂CO₃-controled pH condition, wherease a flocculation of cells was presented after 16h fermentated, which caused the velocity of succinic acid production went down. The effects of nutrition factors on cell growth and production of succinic acid had been studied; the final succinic acid concentration (39g/L) was increased 30% (29g/L) at optimized condition of pH-control with Na₂CO₃, while higher succinic acid yield (90.0%) was achieved (68% befor), respectively, excelled ORP-optimized MgCO₃ pH-control condition(34g/L, 80%)...