Effects of dissolved oxygen and oxygen mass transfer on overexpression of target gene in recombinant E-coli

Overexpression of target gene (MspI 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(-1)p(-1)h(-1)) when the culture was induced with 1 mM isopropyl-beta-D-thiogalactopyranoside (IPTG) in the mid-exponential phase of growth. The maximum value of 6.7 x 10(2) U mg(-1)p(-1) for the target gene expression was attained in about 3 h of postinduction cultivation. An oxygen-sufficient condition (0.22 mmoles l(-1)) was necessary to obtain optimal expression and cell productivity. Expression of the target gene upon induction was accompanied by an increase in oxygen uptake rate (OUR) of the cells and decrease in dissolved oxygen (DO) concentration in the cultivation broth. Volumetric oxygen transfer coefficient (K(L)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. (C) 1997 by Elsevier Science Inc.