| Lactic acid is the most widely occurring hydroxycarboxylic acid which can be used in food, pharmaceutical, textile, leather, and chemical industries. L-lactic acid can be polymerized to polylactic acid (PLA) which is currently a most promising biodegradable plastics without any environmental pollution to replace oil-based traditional plastics. To obtain fermentative production of lactic acid more efficiently, metabolic flux analysis (MFA) can be performed to deeply understand the metabolism of the microorganism.It is necessary to develop a defined culture medium for MFA. In this study, a defined culture medium was optimized based on a semi-synthetic medium for a high lactic acid production strain Lactobacillus paracasei with short growth cycle and tolerance to relatively high concentration of acid. For the seed culture, although we tried to optimize the concentration of amino acid mixtures and metal ions, as well as studied the effect nucleosides addition, we could not obtain a defined medium that can support enough cell growth. For the fermentation culture, the prime components of the medium and the ranges of their concentrations were determined first. Then, the optimal concentration of 6 kinds of nutrients, including glucose, amino acid mixture, nucleosides, vitamins and growth factors, phosphate mixture, and calcium carbonate, was defined through a six factor-five level orthogonal experiment and a subsequent four factor-three level orthogonal experiment, as well as amino acid mixture gradation experiment and amino acid shortage experiment. The final optimized concentrations were:80 g/L glucose,3.925 g/L amino acid mixture,0.15 g/L nucleosides,0.075 g/L vitamins and growth factor,0 g/L phosphate mixture,35 g/L calcium carbonate. A higher cell growth and lactic acid production could be obtained in the optimized defined medium than in the original semi-synthetic medium. All these results provided a basis for metabolic flux analysis in L. paracasei. |
PDF Full Text Request