Summary of Experience and Precautions for Escherichia coli Fermentation

Firstly, the feeding rate and specific growth rate directly affect the generation rate and accumulation amount of acetic acid (mainly the residual sugar content in the fermentation broth is affected by the feeding rate and specific growth rate), so controlling the feeding rate and specific growth rate appropriately has a good effect on controlling the amount of acetic acid.

Secondly, it is necessary to ensure sufficient dissolved oxygen and strictly control the pH value, and the rate of acid-base supplementation should be as gentle as possible, not too fast; Temperature also has a significant impact on protein expression. Proteins produced at lower fermentation temperatures are mostly active, while proteins produced at higher fermentation temperatures mostly exist in the form of inclusion bodies.

Thirdly, selecting a reasonable induction time is very important. Generally, the induction time is chosen in the late stage of exponential growth, and the specific growth rate during induction should be controlled within 0.2. Choosing this time for induction is to separate the rapid growth period of the bacterial body from the protein synthesis period, so that these two stages do not affect each other and are conducive to high protein expression; 2. A large number of bacterial cells have been obtained, and the biomass of the bacterial cells is basically stable, which is reasonable in terms of kinetics, energy consumption, and material cost.

Fourthly, the carbon nitrogen ratio during the feeding process is also important. If the nitrogen source is too high, it will cause the bacterial growth to be too vigorous, the pH to be too high, which is not conducive to the accumulation of metabolites. If the nitrogen source is insufficient, the bacterial reproduction will be reduced, thereby affecting the yield; If there is too much carbon source, it is easy to lower the pH of the execution site, which inhibits the growth of bacterial cells. If there is insufficient carbon source, it is easy to cause bacterial aging and autolysis. In addition, improper carbon nitrogen ratio can also cause bacterial cells to absorb nutrients in proportion, directly affecting their growth and product synthesis.

Based on my own experience, in general, for a stable fermentation process, if the phenomenon of bacterial dissolution always occurs during a fixed fermentation time period and the possibility of bacteriophages and infections can be ruled out, it may be caused by an unreasonable carbon nitrogen ratio. The carbon nitrogen ratio can be adjusted appropriately.