Optimization of metabolic technology for the bioconversion of succinic acid from crop straw

It is very important to optimize the fermentation technology of Actinobacillus succinogenes for the industrial bioconversion of succinic acid from crop straw. Pentose and hexose hydrolyzed from crop straw with hydroxide and enzyme were determined by HPLC. Based on the analysis of metabolic pathway, the fermentation technology was optimized by orthogonal design and response surface methodology. Determination of the hydrolyzate showed that about 52 g glucose and 24 g xylose were hydrolyzed from 200 g crop straw. Metabolic pathway analysis for this strain showed that pentose and hexose could be transferred to succinic acid and other byproducts including acetic acid and α-ketoglutaric acid. On the basis of single factor experiment for primary culture medium ingredient, orthogonal experiment showed that 58 g/L of succinic acid was gained when the concentrations of metal ion and vitamin were as follows(mmol/L): Mg2+ 6.0, Mn2+ 0.9, Fe2+ 0.6, Zn2+ 1.5, VB2 0.005, VB5 0.012, VB14 0.003 and VB12 0.01, respectively. Further response surface analysis indicated the interrelation between those factors including the ratio of CO2 to H2, the concentration of fluoroacetate and pH value. 73 g/L of succinic acid was gained, based on the following optimum conditions: ratio of CO2 to H2 of 30.43, 0.103 mmol/L of fluoroacetate and pH 5.51. The yield of succinic acid increases by 25 g/L and the strain Actinobacillus succinogenes HF-7 has good application of industrial fermentation.