Physiological and Morphological Changes of Recombinant E. coli During Over-Expression of Human Interferon-g in HCDC

The objective of this research was to investigate the influence of the over-expression of recombinant interferon-g during high cell density cultivation on cellular characteristics of recombinant E. coli. Batch and fed-batch culture techniques were employed to grow Escherichia coli BL21 for production of human gamma-interferon in pET expression system. Final cell densities in batch and fed-batch cultivations were approximately 7 and 127 g cell dry weight (CDW) l-1, respectively. In both systems, specific growth rate decreased and reached zero, 4 hours after the induction. It was found that high cell density and over-expression of interferon-g had no substantial effects on cell lysis and plasmid stability. Plasmid content of the cells was nearly similar and remained constant during the post-induction period in both batch and fed-batch cultures (60 mg plasmid per g-1 CDW). In both systems, time profiles of acetate and lactate production were similar, lactate concentration was lower than that of acetate and the concentrations of both were lower than the inhibitory level. Maximum extracellular cAMP concentration occurred at the start of induction in fed-batch culture and was higher than the amount produced during the batch process. The size of E. coli cells reduced significantly as cell density increased and the morphology of the cells in high cell density changed from the usual rod shape to spherical, while the expression of interferon-g remained almost constant.