Effect Of Amino Acid On Growth And Expressing Recombinant Protein Of E.Coli BL21

Initially, influence of concentration of inorganic nitrogen on growth of E.coli was investigated and several kinds of nitrogen-limited media were established. Under the nitrogen-limited circumstance, with the inorganic nitrogen source as control, effect of organic nitrogen on growth of the microorganism was examined and optimization of induction time and dose of inducer was conducted. The results showed that complex organic nitrogen did not only promote its growth, but also its recombinant protein. Subsequently, impact of free amino acids on its growth and producing of recombinant protein in the synthetic media was conducted. It turned out that under some certain conditions, some free amino acids could boost the growth of E.coli and its expression of recombinant protein compared with inorganic nitrogen. Through deep analysis, the fact that amino acids could promote the growth and recombinant protein may have some relevance with relA gene, which encodes ppGpp synthetase. For further study, Red recombination system was utilized to inactive the gene and similar research was conducted with this new mutant. The result illustrates that many amino acids which could be able to promote the growth of wild type strain cannot facilitate its growth once the relA was deleted. In addition, this mutant was not as robust as the wild type strain regarding on producing recombinant protein even though within the LB media which could enbale the two strains grow equivalently. Overall, relA gene was of great significance in terms of the promoted effect of amino acids on the growth and expression of recombinant protein.