A novel strategy to increase protein expression yield is unintended induction of expression in complex media, called auto-induction. This method can be used to express proteins under control of the lac promoter without any need to monitor bacterial growth pattern, and addition of specific expression inducers such as Isopropyl β-D-1-thiogalactopyranoside (IPTG) at proper time. In the present study, a codon optimized gene encoding granulocyte-macrophage colony stimulating factor (GM-CSF) was cloned and over-expressed in Escherichia coli BL21 (DE3) using both conventional inducer-based and auto-induction approaches in a shake flask scale and the yield of GM-CSF expression and biomass production was identified. Results showed higher biomass production and expression yield for GM-CSF in case of auto-induction comparing with IPTG-induction. The auto-induction approach was also performed in a fed batch fermentation process in a 2-L bioreactor scale. The feeding strategy yielded an amount of 300 mg/L GM-CSF within 20 h of induction. However, most of the over-expressed GM-CSF was produced as inclusion bodies and following purification and refolding, a final yield of 90 mg/L was achieved. These results suggest that auto-induction approach can be effectively applied in fed-batch fermentation for the large scale production of GM-CSF; however, further optimization of purification process is obligatory to increase the purification yield.
Keywords: Auto-induction; Escherichia coli; Granulocyte-macrophage colony-stimulating factor; Inclusion bodies; Overexpression..