A CONDITIONAL SUICIDE SYSTEM IN ESCHERICHIA-COLI BASED ON THE INTRACELLULAR DEGRADATION OF DNA

The potential risks associated with the intentional or unintentional r elease of genetically engineered microorganisms led to the constructio n of biological containment systems by which bacteria are killed in a controlled suicide process. In previously published suicide systems, c ell killing was caused by proteins destroying the cell membrane or cel l wall. Here a conditional cell killing system based on the intracellu lar degradation of cellular DNA is presented. The nuclease gene used w as that of the extracellular nuclease of Serratia marcescens. The nucl ease gene was deleted for the leader-coding sequence, and the truncate d gene was put under the control of the lambda p(L) promoter. Followin g thermoinduction of the nuclease gene cassette in Escherichia coli, c ell survival dropped to 2 x 10(-5), and more than 80% of the radioacti vely labeled DNA was converted to acid-soluble material within 2.5 h i n the absence of cell lysis. The majority (84%) of clones which surviv ed thermoinduced killing turned out to be as sensitive to a second the rmoinduction as the original strain. The other clones showed somewhat slower killing kinetics or slightly higher final levels of survivors, The suicide system described combines the regulated killing of cells w ith the destruction of intracellular DNA otherwise potentially availab le for horizontal gene transfer processes.