The Lactic Acid Generating Bacteria's Fermentation Regulation And Molecular Modification

In this paper, classification, uses, method of fermentation and production of lactic acid were introduced. Several lactic acid bacteria strains are used to study the optimum fermentation conditions which respectively used Glucose and xylose as carbon source of lactic acid fermentation medium.In the current leweal of study, it is very difficult to get 100% optical purity of lactic acid. There have been reports about pH, temperature, nitrogen and sugar concentration of such factors as the ammount of fermentation conditions for the initial study to observe the ammount of lactic acid and the optical purity of the product. In this study, several lactic acid bacteria strains are used to study the fermentation control method to obtain a higher optical purity, lower cost and greater production of the product of the ammount of lactic acid on the basis of optimum fermentation conditions. Studying the effect of cultivation conditions on the optical purity of adding lactate in the initial fermentation medium by Rhizopus oryzae, Lactobacillus and Escherichia coli.The effect of cultivation conditions on the optical purity of L-lactic acid produced by Rhizopus oryzae was investigated. The isomeric composition of lactic acid was influenced by the supplementation of L-lactic acid to fermentation medium. L-isomer increased with the dosage, no D-lactic acid was observed when the concentration of supplemented L-lactic acid in matrix was≥1.5 g/L. However, the L-lactic acid yield, biomass and glucose conversion rate decreased with the dosage. As the same method, the supplementation of L-lactic acid to substrate was a little efficient for influence isomeric composition of lactic acid by Escherichia coli and Lactobacillus.We used Co-60 mutation method to improve the production of D-lactic acid producted by Escherichia coli. Based on studies and comparisons, we selected D-lactic acid high-yielding strain. In order to take advantage of xylose and to improve the utilization of xylose and the production of L-lactic acid, were egenetically modified the E.coli W3110.The key gene: xylB,talA,tktA,xylA.