Influence of culture conditions on the growth of Escherichia coli

Influence of culture conditions on the growth of Escherichia coli

The use of E. coli to produce medicines is a biological method. That is, the use of bioengineering technology to transfer foreign genes into E. coli, fermentation and culture for expression, centrifugation to collect the bacteria, and then use a specific solution to break the bacteria and collect them. The target protein is made into medicine after some subsequent processing.

1. Culture temperature

Experiments show that the optimal culture temperature is within the range of 35~40℃, and the cell density increases with the increase of temperature, which is consistent with the general growth characteristics of E. coli. However, the growth rate is faster at 37℃~38℃, and the subsequent growth is relatively flat. Combining the general culture characteristics of E. coli and the cross-influence of temperature and other influencing factors, the culture temperature was set at 37.5°C in the experiment.

2. pH value

After culturing E. coli for 18h with different pH values, the test results show that the pH value of 8.0 has no significant effect on the cell density, and the pH value is too low or too high to achieve good results . When the pH value is 7.5, the cell density is relatively highest, and its OD600nm reaches 3.25.

3. The influence of dissolved oxygen on the growth of bacteria

According to the different dissolved oxygen index in the fermentor, the cell density of the fermentation system when cultured for 18 hours was obtained. Experimental results show that the cell density increases continuously with the increase in the dissolved oxygen index, but the cell density increases slowly after 50%.

4. Influence of inoculation amount

Optimizing different inoculation amounts can have a greater impact on the growth of bacteria. At 3% to 4%, the growth state of bacteria is better than that of too low or high inoculation amounts. Too low inoculation amounts will make the growth of bacteria too slow. Too high inoculum amount will consume a large amount of nutrients in the early stage and cause a waste of seed strains, so 4% inoculum amount was used in the experiment.

5. Determination of culture time

The experimental results of different incubation times showed that the bacteria increased by multiples from 12 to 18 hours, and then grew slowly. It shows that in the later stage of exponential growth, the energy of bacteria is not suitable for mass reproduction, but is affected by metabolites. Therefore, in order to shorten the growth cycle, the harvest of bacteria should be in the late exponential growth period, that is, 18h.

6. Determination of speed

The speed of the shaking incubator increases with the increase of dissolved oxygen and the cell density increases accordingly. The growth rate of the cell density is faster at 100~200r/min, and relatively slow at 200~300r/min, indicating that the speed of 200r/min can already promote the dissolution of oxygen in the air. Taking into account that the increase of the speed may produce adverse effects such as foam, so the best speed adopted in the test is 200r/min.

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