The effects of lactose induction and LacI on a plasmid-free Escherichia coli T7 expression system

Abstract

For the production of antigen binding fragments (Fabs) in E. coli, plasmid-based expression systems are predominantly used and Isopropyl-β-D-thiogalactopyranoside (IPTG) is applied to induce recombinant protein production. Such processes are known to put increased metabolic stress on the cells, resulting in less viable cells and less productivity. Previous studies have pointed out the advantages of lactose as an inducer concerning cell viability and productivity, others have shown the benefits of plasmid-free expression systems, where the gene of interest (GOI) is integrated into the host cell chromosome. In this study we attempt to combine the advantages of lactose induction with a plasmid-free expression system in E. coli BL21(DE3). We determine the feasibility of such processes, record a mechanistic correlation of the maximum specific lactose uptake rate and the specific glucose uptake rate of such an expression system and evaluate the effects on cell viability and productivity of soluble product, in order to compare them to an IPTG-induced reference process. Furthermore, we establish new platform knowledge concerning the influence of the lac-repressor (LacI) on the lactose induction of plasmid-free expression systems.