Optimization of culture conditions in CO ₂ fixation for succinic acid production using Actinobacillus succinogenes

The culture conditions in CO ₂ fixation by Actinobacillus succinogenes for succinic acid production were investigated by a model of available CO ₂ in a 3-l fermentor. The results from the model analysis showed that the available CO ₂ for succinic acid production in the fermentation broth is the sum of HCO ₃ ^-, CO ₃ ^2-, and CO ₂ influenced by external culture conditions such as medium components, CO ₂ partial pressures, and temperature. The optimized conditions for CO ₂ supply in a 3-l fermentor were determined as follows: CO ₂ partial pressure and stirring speed were maintained at 0.1 MPa and 200 r min ^-1, respectively, with a pH of 6.8 and a temperature of 37°C; 0.15 mol l ^-1 NaHCO ₃ was added. Under the optimized conditions, a CO ₂ fixation rate of 0.57 g l ^-1 h ^-1 was obtained, and a succinic acid concentration of 51.6 g l ^-1 with a yield of 75.8% was reached. These results suggest that optimized conditions of CO ₂ supply are effective in high succinic acid production and thus have potential applications in succinic acid production and CO ₂ fixation.