Recombinant E. coli; IFTG induction; Bioreactor; Dissolved oxygen level; Oxygen mass transfer; Expression of cloned gene
Overexpression of target gene (Mspl methylase) in recombinant Escherichia coli has been studied in response to dissolved oxygen and oxygen mass transfer. The rate of target gene expression attained its maximum value (2.67 U mg-1p-1h-1) when the culture was induced with 1 llzM isopropyl+-o-thiogalactopyranoside (IPTG) in the
mid-exponential phase of growth. The maximum value of 6.7 x ld U mg-1p-1 for the target gene expression was attained in about 3 h ofpostinduction cultivation. An oxygen-suficient condition (0.22 mmoles I-1) was necessary
to obtain optimal expression and cell productivity. Expression of the target gene upon induction was accompa-nied by an increase in oxygen uptake rate (OUR) of the cells and decrease in dissolved oxygen (DO) concen-
tration in the cultivation broth. Volumetric oxygen transfer coeficient (K,a) of 61 h-1 was optimum for cell productivity of uninduced culture while that for induced culture was 84 h-1 which was optimum for foreign protein synthesis also.