Evaluation of heat induction strategy for recombinant human growth hormone expression in fed-batch fermentation

The high cell density cultivation (HCDC) of a recombinant E. coli producing human growth hormone (hGH) under different heat induction strategies has been reported. In this paper the effect of heat shock temperature, its duration and post-induction temperature, at two levels on cell growth and death, hGH production and its degradation, substrate utilization and by-product formation were investigated by full factorial experimental design. The results showed that heat shock temperature was the most effective factor on hGH production having approximately 75.8% of total contribution. There was no significant accumulation of substrate or by-product in culture medium during HCDC in all experiments. Thirty two percent of cells were subjected to lysis during the heat induction at 42°C for 20 min followed by 37°C for 4h. Biologically active recombinant hGH was produced comprising 13% of total cell protein without degradation. An empirical equation was employed to describe the relationship between three factors and hGH production during HCDC.