The effect of organic nitrogen and glucose on the production of recombinant human insulin-like growth factor in high cell densityEscherichia coli fermentations

Two kinds of fed batch fermentation processes were compared at a 10-liter scale to examine their effect on recombinant human insulin-like growth factor (IGF-1) gene expression in Escherichia coli.The difference between the two processes was the feed medium composition and whether the process used a single or dual feed during the course of the fermentation.In the dual feed system, organic nitrogen was delivered at a higher rate (50 g/h) than in the single feed system (5 g/h).The dual feed process resulted in a significant increase in IGF-1 yield.30 mg IGF-t/g dry cell weight was synthesized in the dual feed system compared to 3 mg IGF-1/g dry cell weight obtained in the single feed system.The presence of high levels of organic nitrogen during the induction period may enhance IGF-1 synthesis by protecting the IGF-1 from proteolytic degradation.The IGF-1 yield decreased to 17 mg/g dry cell weight when the glucose supply was decreased from 17 g/h to 8 g/h during the induction period; however, an increase in glucose supply from 17 g/h to 50 g/h during the induction period did not enhance the IGF-1 synthesis.Thus, the enhancement of IGF-1 gene expression in the dual feed process was mainly dependent on a high level of organic nitrogen and an appropriate level of glucose in the medium during the induction period.