Mutation-screening High Yield L-lactic Acid Strain
|School||Henan University of Science and Technology|
|Course||Biochemistry and Molecular Biology|
|Keywords||L-lactic Mutation Breeding Medium Optimization|
L-lactic acid is an important organic acid, widely used in food, pharmaceutical, chemical and other industries. Especially in recent years biodegradable polymer materials - the development of polylactic acid of L-lactic acid in the market demand increasing. In this paper, Lactobacillus casei CICC6028 for the original strain, first of all medium and culture process optimization. The results show that the seed culture 24h, inoculation amount of 10%, pH 6.8, culture temperature 34 ° C Fermentation medium composition (g / L): glucose 140, beef extract, yeast extract 4.5, peptone, dried over anhydrous sodium acetate 5 , MgSO 4 · 7H2O 0.2, MnSO 4 0.125, Tween -80 1mL, the CaCO 3 50 lactic acid production reached 90.7g / L. Mutagen test strain using ultraviolet, microwave, diethyl sulfate, low energy ion beam, etc. repeated mutagenic treatment to obtain the best of each of the mutagen mutagenesis parameters were as follows: UV lamp power of 15W, the sample from the lamp distance 15cm deal with 15s; microwave power 480W, intermittent mutagenesis the way handled a total of 40s; the diethyl sulfate concentration of 1%, processing 30min; ion beam energy 10Kev, doses of 50 × 2.6 × 10 13 sup>. Using the above best mutagenesis parameter of the test strains repeatedly Mutation Breeding, screening out a high-yielding mutant strain NE-19, its lactic acid production reached 121.3g / L, 33.7% higher than the original strain. Discovered mutant strains of L-lactic acid production by different temperature, lactate production when the incubation temperature of 40 ° C highest mutant optimum fermentation temperature of 40 ° C is. HPLC analysis found that the fermentation product is a lactic acid of the mutant strain almost no other byproducts generated metabolites yielding mutant strains. By response surface optimization of the carbon and nitrogen sources in the fermentation medium of the mutant strains, finally get to the top of the fermentation medium (g / L): Glucose 153.7, peptone 17.3 beef extract, 15.9, yeast extract 8.3, anhydrous acetic acid sodium 5, MgSO 4 · the 7H 2 O 0.2 the MnSO 4 0.125, Tween -80 1mL, CaCO 3 50, pH 6.8. Optimized medium after the verification test, the results show that the mutant strain of lactic acid production averaged 134.00 ± 2.59g / L. The mutant starting fermentation kinetic curves of mutant accumulation of L-lactic acid production and sugar consumption is faster than the original strain, fermentation arrive 120h, mutant strain of lactic acid production reached 142g / L, residual sugar only 3.6g / L, starting strain of lactic acid production only 98g / L residual sugar content was as high as 43.7g / L, the mutant is an ideal of L-lactic acid production strains.