Conditional Suicide System for Containment of Bacteria and Plasmids

Abstract

The design of biological containment systems to be employed in a broad spectrum of bacteria useful in industrial fermentations and in connection with release to the environment is reported. The key element is a gene, hok, encoding a small polypeptide of 52 amino acids that is lethal when expressed in a variety of bacterial species. Constructing combinations of regulatable promoters and this toxin gene has allowed us to design model systems that in simple ways ensure cell survival under controlled conditions (the fermenter), whereas any cells accidentally escaping to the environment, or any other new combination of a bacterium and the toxin-carrying plasmid, will be killed. A specific application of the containment system with respect to deliberate release is based on a fusion between an invertible promoter and the toxin gene. This results in a stochastic induction of the killing function, which will lead to the elimination of the organism as a consequence of competition with related bacteria in the environment.