A high content of yeast extract in complex media can cause auto-induction of phage T7 RNA polymerase and the consequent expression of recombinant protein in Escherichia coli BL21(DE3) during long-term cultivation. Our study demonstrated that the auto-induction of recombinant protein varied in different vectors harboring heterologous genes. Trx, GST, and their fusion proteins such as GST-human parathyroid hormone (hPTH), expressed by pET32a (+), were easily auto-induced by media containing a high content of yeast extract; however, rtPA was not easily auto-induced when using pET22b (+), although both pET systems were under the control of T7lac promoter. Furthermore, the auto-induction of GST-hPTH may start within 1-2 h after inoculation in bioreactors, which is a deficiency in the scale-up from shake flasks to bioreactors. Our results indicated that too much yeast extract in bioreactor cultivations may be responsible for the early auto-induction of target proteins and consequent loss of cell viability and plasmid instability. To achieve a satisfactory yield, host cells with both high cell viability and plasmid stability were necessary for the starter cultures in shake flasks and pre-induction cultures in bioreactors. This could be achieved simply by controlling the initial content of yeast extract and its subsequent supplementation.
1.Chinese Acad Sci, Mol Cell Biol Lab, Inst Biochem & Cell Biol, Shanghai Inst Biol Sci, Shanghai 200031, Peoples R China 2.Chinese Acad Sci, State Key Lab Phytochem & Plant Resources W China, Ctr Drug Screening & Res, Kunming Inst Bot, Kunming 650204, Yunnan, Peoples R China 3.Shanghai Jiao Tong Univ, Key Lab Microbial Metab, Minist Educ, Sch Life Sci, Shanghai 200240, Peoples R China
Recommended Citation:
Jia, LH; Cheng, HR; Wang, HW; Luo, HR; Yan, H.From shake flasks to bioreactors: survival of E. coli cells harboring pGST-hPTH through auto-induction by controlling initial content of yeast extract,APPLIED MICROBIOLOGY AND BIOTECHNOLOGY,2011,90(4):1419-1428
