Restricting the dispersal of recombinant DNA: design of a contained biological catalyst

To restrict horizontal gene spread and, thus, create organisms whose behavior in the field is more predictable, we have combined a mini-Tn5 cloning system that allows stable insertion of foreign genes into the chromosomes of a variety of Gram-negative bacteria with a gene-containment circuit based on the universal lethal-function colicin E3. Use of the system is exemplified by the construction of a micro-organism designed to degrade polychlorinated biphenyls, important environmental pollutants. The relevant genotype of the microorganism is subject to a stringent gene-containment mechanism that provides neither an advantage nor a disadvantage to the host cell for survival, but decreases frequencies of productive chromosomal transfer frequencies by at least four orders of magnitude.