Cells may obtain mutation during cell division. Mutations and deletion of the entire system allow cells to have lower metabolic burden, and hence have a faster speed of division. The mutated cells may then easily take over the entire population. Superbug may also be produced when mutation accumulate.
Hence, to ensure safety, we designed a kill switch to target the cells with mutation in / deletion of our cre-lox system. We include a domain coding for anti-toxin in between the two terminators, and let the cell express toxin at the same time. When there is mutation or deletion of the system, antitoxin do not get expressed, and the cell will die due to the toxin produced. With this toxin-antitoxin system, we can eliminate mutated cells.
On the other hand, we can also put the code for toxin outside our lox pair, so when there is deletion, promoter can trigger the expression of toxin, leading to the death of cells that underwent deletion mutation.
KILL SWITCH MODEL SIMULATION
BEFORE: tf = 20, tr = 20, tm =15, w/o kill switch
AFTER: tf = 20, tr = 20, tm =15, w/ kill switch
When the cells are left to mutate, the mutant cells soon dominates the culture after around 250 min (left figures). By simulating our kill swtich model with a 99% killing rate, we can effectively suppress the growth of mutant cells and hence delay the time when the mutant cells will dominate the population.