Cold-sensitive E-lysis systems

The release of recombinant bacteria into the environment is undesirable because of possible risks associated with the genetically modified organisms. The aim of this study was to establish a cold-sensitive killing system with a lethal gene, activated when bacteria encounter lower environmental temperatures. To obtain cold-sensitive lysis vectors, the λcI857 repressor/ p R promoter expression system was combined with either the lacI/ lacZpo or the phage 434 cI/ p R system that control the expression of the lysis gene E of bacteriophage φX174. Escherichia coli strains harbouring such suicide vectors are able to grow at 37°C, but cell lysis takes place at temperatures below 30°C. By replacing gene E with a β-galactosidase reporter gene we also showed that the onset of β-galactosidase activity corresponds with the onset of lysis at 28°C. Results indicate that these newly combined promoter/repressor systems can also be used to confer cold-sensitive expression to any gene of interest.