Kinetics of inclusion body production in batch and high cell density fed-batch culture of Escherichia coli expressing ovine growth hormone.

A process for maximizing the volumetric productivity of recombinant ovine growth hormone (r-oGH) expressed in Escherichia coli during high cell density fermentation process has been devised. Kinetics of r-oGH expression as inclusion bodies and its effect on specific growth rates of E. coli cells were monitored during batch fermentation process. It was observed that during r-oGH expression in E. coli, the specific growth rate of the culture became an intrinsic property of the cells which reduced in a programmed manner upon induction. Nutrient feeding during protein expression phase of the fed-batch process was designed according to the reduction in specific growth rate of the culture. By feeding yeast extract along with glucose during fed-batch operation, high cell growth with very little accumulation of acetic acid was observed. Use of yeast extract helped in maintaining high specific cellular protein yield which resulted in high volumetric productivity of r-oGH. In 16 h of fed-batch fermentation, 3.2 g l-1 of r-oGH were produced at a cell OD of 124. This is the highest concentration of r-oGH reported to date using E. coli expression system. The volumetric productivity of r-oGH was 0.2 g l-1 h-1, which is also the highest value reported for any therapeutic protein using IPTG inducible expression system in a single stage fed-batch process.