High-yield Production of Granulocyte-macrophage Colony-stimulating Factor in BL21 (DE3) By an Auto-induction Strategy.

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 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 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.