The Optimization Of Succinic Acid Producing Strain

Succinic acid is a widely used organic chemical product.It can be used as raw materials for chemical synthesis or intermediate products or reaction substrates in the production process.It is widely used in pharmaceutical,food additives,green solvents and degradable plastics and other fields.In nature,prokaryotic microorganisms are easy to cultivate and control because of their fast metabolism and rapid propagation,and can quickly metabolize the target products or bacterial metabolites we need.Therefore,we choose Escherichia coli strains as the microbial strains for succinic acid production.In this study,a strain of Escherichia coli with initial yield of 1.51 g/L was used as the starting strain,and different biological mutagenesis methods,such as ultraviolet ray mutagenesis,microwave mutagenesis and DES chemical mutagenesis,were used to mutagenesis a strain with succinic acid production of 37.08 g/L.After ten generations of generation,the stability of the product was tested.Then we carried on the further experiment through a series of optimization design methods,such as single factor and response surface condition,and we got the finally the optimum medium composition in the experiment is glucose 5%,ammonium sulfate 0.8%,peptone 0.4%,magnesium sulfate 0.06%,calcium carbonate2%,potassium chloride 0.06%,potassium dihydrogen phosphate 0.4%,and succinic acid output reaches as high as 5%.At 41.89 g/L,it was proved that the yield of succinic acid reached 47 g/L.The fermentation conditions of succinic acid production by Escherichia coli strain HX3 were optimized.The fermentation conditions were 80 m L per 250 m L triangular bottle,the initial p H value in the medium was adjusted to 6.0,and the optimal inoculum volume was 4%.When the fermentation time was about 42 h,the yield of succinic acid was the highest,which could reach 51 g/L is about 33 times the amount of acid produced by the initial strain.After the completion of the breeding work,we further carried out the industrial scale-up verification experiment of the selected strains.Through the step-by-step scale-up experiment of 10 L,100 L and 1 m3 fermenter,the succinic acid production of the final strain of Escherichia coli HX3 was stable at 55 g/L,which has a certainindustrial production potential.