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 lambdacI857 repressor/pR promoter expression system was combined with either the lacI/lacZpo or the phage 434 cI/pR system that control the expression of the lysis gene E of bacteriophage phiX174. Escherichia coli strains harbouring such suicide vectors are able to grow at 37 degrees C, but cell lysis takes place at temperatures below 30 degrees C. By replacing gene E with a beta-galactosidase reporter gene we also showed that the onset of beta-galactosidase activity corresponds with the onset of lysis at 28 degrees C. Results indicate that these newly combined promoter/repressor systems can also be used to confer cold-sensitive expression to any gene of interest.