A Taguchi approach for optimizing the expression of recombinant human growth hormone in Escherichia coli

Expression of recombinant human growth hormone in E. coli requires specific measures to be more efficient. In this study, two strains of E. coli, one with a genomic expression of T7 and arabinose promoters and the other with a plasmid expression (T7 promoter), were examined. In this regard, the appropriate time for sampling strains carrying the rhGH gene in genomic or plasmid form was tested. First, the best time to add the inducer to the culture medium and different concentrations of arabinose and IPTG inducers were investigated. Separate and simultaneous use of both inducers in strains with both promoters was investigated. Next, the strains were studied in five different culture media, and TB was selected as the optimal culture medium. Finally, the optimal expression of recombinant protein in TB medium was investigated using the Taguchi test for three parameters of peptone casein, yeast extract, and glucose at three different levels. Results showed the best sampling time in genomic strains was overnight; however, in plasmid strains, it was 4 hours after induction. The best time to add the inducer in genomic strains was at the beginning of the exponential phase of bacterial growth. Furthermore, lower amounts of antibiotics were associated with higher amounts of recombinant protein production in genomic strains. In the strains that had both are and T7 promoters, simultaneous induction with both inducers, i.e., arabinose and IPTG resulted in more protein expression than the single inducer.