Cultivate Genetically Engineered Bacteria To Study The Expression Of Thymosin ¦Á1 Fusion Protein

The cultivation of the recombinant E. coli BL21(DE3) which carries heterogeneous gene coded for thymosin αl was carried out in shake flasks. The effects of medium composition, the initial concentration of glucose, the inducer concentration and the inducing time required on the growth of the recombinant E. coli and heterogeneous protein expression were investigated, respectively. The results showed that the temperature suitable for the growth of this recombinant strain and fusion protein expression are 35 - 37癈 and 30 癈. The media contained of sugar is benefit for the recombinant E. coli growth. Using ITPG as an inducer, the inducing should be started at the middle of exponential growth phase. Controlling the inducer concentration of 0.4 - 0.5 mmol/L and inducing time of 4 - 6h, a high hetergeneous protein expression level of 26 - 28% based on the total protein is achieved.Furthermore, high density culture of the recombinant E. coli was carried out using a standard stirred bioreactor with a working volume of 5L. The results showed although the feeding of glucose is benefit to the growth of the recombinant E. coli and a density of 16 g (d.w.)/L was achieved, the express level of heterogeneous protein is decreased obviously because of acetic acid formation due to the recombinant E. coli overgrowth which resulted in the oxygen mass transfer limitation. Therefore, a glucose feeding strategy should be optimized in order to achieve both high cell density and high level expression of heterogeneous protein. Finally, the growth kinetics of the recombinant E. coli was developed based on the Monod equation as follows:...