No abstract

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.

This study investigated the influence of osmotic stress on succinic acid production by Actinobacillus succinogenes NJ113. Both cell growth and succinic acid production were inhibited with the increase in osmotic stress of the medium. The use of three different osmoprotectants in the production of succinic acid was studied in order to decrease the inhibitory effects of osmotic stress during fermentation. Results indicated that proline offers optimal osmoprotection in the production of succinic acid by A. succinogenes NJ113. In tests of batch fermentation, the maximum cell concentration was observed to be 5.36 g DCW/L after the addition of 25 mmol/L proline to the fermentation medium. The cell concentration was 24% higher than that noted for the control. A total quantity of 56.2 g/L of succinic acid was produced, with a production rate of 1 g/L per hour, after 56 h of fermentation. The concentration and productivity of succinic acid was observed to be increased by 22.2% and 22%, respectively, as compared with the control. The specific activity levels of key enzymes in the metabolic network was noted to be higher following the addition of proline, particularly in the later stages of fermentation. This method of enhancing succinic acid production by the addition of an osmoprotectant may potentially provide an alternative approach for enhanced production of other organic acids.

Fermentation and succinic acid production by Actinobacillus succinogenes YZ0819 was inhibited by high NaCl. To enhance the resistance of this strain to osmotic stress, an NaCl-tolerant mutant strain of A. succinogenes (CH050) was screened and selected through a continuous culture using survival in 0.7 M NaCl as the selection criterion. Using Na 2 CO 3 as the pH regulator and glucose as the carbon source in batch fermentation, the isolated osmoresistant stain, A. succinogenes CH050, produced up to 66 g/l succinic acid with a yield of 73.37% (w/w). The concentration of succinic acid and mass yield were increased by 37.5 and 4.37%, respectively, compared to the parent strain. The dry cell weight reached 10.1 g/l, which is 37% higher than that of the parent strain. The high tolerance of A. succinogenes CH050 to osmotic stress increased improved the succinic acid production from batch fermentation.