CcdB destroys the DNA gyrase of engineered bacteria. In a non-laboratory environment without the application of tetracycline, the PgapA promoter stops driving the antitoxin CcdA, and the normally released toxin CcdB disrupts DNA replication, causing the engineered bacteria to stop growing or die, thus achieving biosafety control.

In the laboratory environment, tetracycline is applied, and the PgapA promoter drives the release of the antitoxin CcdA. The antitoxin CcdA binds to the toxin CcdB, blocking the destruction of the DNA gyrase of the engineered bacteria by CcdB. The complex negatively feedback regulates its own expression, ensuring the normal proliferation of the engineered bacteria to efficiently degrade OTA.