Impact of plasmid size on cellular oxygen demand in Escherichia coli

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Abstract
Escherichia coli DH5α harbouring either pBGS18, a 4.4 kb pUC‐based plasmid, or pQR150, a 20 kb derivative of pBGS18, were grown in glucose‐limited chemostat culture to investigate the effects of plasmid size and recombinant protein production on oxygen demand. Under non‐induced conditions, where no recombinant protein was expressed, the cellular oxygen demand of cells harbouring pBGS18 and pQR150 was not significantly different, mean specific oxygen uptake rate (OUR) being 0.75±0.24 and 0.78±0.32 mmol/h per mg of plasmid respectively. Under isopropyl β‐d‐thiogalactoside‐induced conditions, where recombinant protein was expressed, cells harbouring pBGS18 demonstrated a statistically insignificant 37% increase in mean specific OUR while those harbouring pQR150 demonstrated a statistically significant 415% increase. It is concluded that plasmid size does not significantly affect oxygen demand and that increasing oxygen demand observed with increasing plasmid size is due to production of recombinant protein.