Breeding And Fermentation Condition Optimization Of D-lactic Acid Producing Bacillus Laevolacticus Strains

D-lactic acid has been widely used in pharmaceutical, biomedical engineering, industrial, high efficiency and low toxicity pesticides, the synthesis of polylactic acid and spices. Global demand for D- lactic acid is growing at a rate of 6%-8% annual. In recent years, the demand for D- lactic acid increases daily with the further promotion of polylactic acid market. In this paper, Pseudomesenteroides leuconostoc, Lactobacillus bulgaricus, Bacillus laevolacticus which conserved in the laboratory were researched to carry out mutation breeding and fermentation condition optimization of D-lactic acid production bacteria. The main results are as follows:1. The optimum temperature for growth of Pseudomesenteroides leuconostoc was 35℃.The initial glucose concentration was 4%.The optimum pH was 6.5.The inoculation quantity was 6%.The optimum temperature of acid production was 35℃.The fastest consumption of sugar was at 35℃. Under the optimum conditions the acid production was 10.9g/L. The optimum temperature for growth of Lactobacillus bulgaricus was 37℃.The initial glucose concentration was 4%.The optimum pH was 6.5.The inoculation quantity was 8%.The optimum temperature of acid production was 37℃.The fastest consumption of sugar was at 37℃. Under the optimum conditions the acid production was 13.3g/L.The optimum temperature for growth of Bacillus laevolacticus was 37℃.The initial glucose concentration was 3.5%.The optimum pH was 7.0.The inoculation quantity was 10%.The optimum temperature of acid production was 37℃.The fastest consumption of sugar was at 37℃. Under the optimum conditions the acid production was 29.7g/L. Acid production of Bacillus laevolacticus was higher, and Bacillus laevolacticus was determined as the optimal strain for D-lactic acid production.2. Bacillus subtilis was treated by the combination of the UV and sodium nitrite mutagenesis to determine the optimum conditions. The results were as follows: UV mutagenesis time was 90 s and sodium nitrite mutagenesis time was 30 min. The acid production of mutant strain W-1 was stabilized at 54g/L, 81.8% higher than the original strain.3. The fermentation conditions of Mutagenized LLA Bacillus W-1 were optimized, and the optimum conditions were: the fermentation temperature was 37 ℃, the concentration of sugar was 90g/L, the nitrogen content was 5g/L, the acid production reached the maximum 60g/L when the inoculation quantity was 10%, 11.1% higher than W-1 strain.4. The effect of corn straw as a carbon source supplement on the fermentation of W-1 strain for D-lactic acid production was investigated, and the results were as follows: when the glucose concentration was 90g/L, nitrogen content was 5g/L, inoculation amount was 10%, corn stalks pretreated with the method of high-temperature cooking- enzymatic hydrolysis was 30%, the amount of cellulase enzyme was 300U/L and 37 ℃fermention for 6d, the acid production reached the highest 72g/L, which increased by 142% compared with the original strain.