An auto-inducible Escherichia coli lysis system controlled by magnesium.

The Escherichia coli (E. coli) prokaryotic expression system is widely used in the field of biology. The currently adopted processes for inducing cell wall rupture, in order to release the target protein, are complex and cumbersome. We developed an auto-inducible E. coli lysis system that is regulated by exogenous magnesium ion (Mg(2+)) concentration. This system is composed of a strictly Mg(2+)-regulated promoter Pmgt from the mgtB gene of Salmonella typhimurium, and the lysis genes from lambda bacteriophage. Both the wild type and Sam7-mutant lysis genes were inducibly expressed in E. coli under Mg(2+)-depleted conditions. The former caused a rapid lysis, while the latter induced very mild lysis of the host strains. However, rapid lysis was observed when the latter was resuspended in Tris-EDTA buffer. Finally, the inducible lysis cassette containing wild type lysis gene was introduced into an expression plasmid expressing GFP gene and efficient lysis of the host E. coli strain and subsequent release of the target protein was achieved in Mg(2+)-depleted conditions. Collectively, the current study indicates that this novel inducible lysis system could have attractive applications in the field of protein expression and provides new insights for the development of bacterium-based vaccines.