Where’s Plasmo?

Our project can be compared to the concept of the popular children’s book, “Where’s Waldo?” that consists of pages depicting large images of almost identical looking people and characters in various situations, and the challenge for readers is to find Waldo somewhere in this crowd. Waldo wears a red and white striped shirt and is often quite hard to recognize in the sea of stripes, red, and white. Plasmo is the bacterial version of Waldo.

Our biocontainment project is based upon the idea of using a plasmid-loss genetic safeguard. Normally, “kill-switches” are used as the go-to mechanism for genetic safeguards. However, kill-switches are problematic because they impose selective pressure on a population of synthetic organisms to evolve resistance to kill-switches. In the aftermath of a kill switch activation, only the resistant mutants remain (represented by Plasmo) and they replicate to form a large population of Plasmos.

In our alternative approach, the plasmid-loss genetic safeguard system, the genetically engineered traits are removed from the population of bacteria using a "self-deleting" CRISPR/Cas9 plasmid. In the end, the population with it's plasmid deleted is indistinguishable from the wild-type population. Since there are still so many wild-type bacteria in the population, the Plasmos are lost among them. They are so few compared to the wild-type bacteria that you can barely find them anymore!

We propose this as a safer mechanism for using synthetic organisms outside of laboratory settings, so that the environment is not overrun by tons of Plasmos!