QCODE biocontainment system for engineered strain protection. (A) Introduction of Q-codons into essential enzymes regulates cell growth via the QCODE system, ensuring engineered strain protection. (B) Strains carrying the Q-codon in the essential genes showed cell growth exclusively in the active QCODE condition. (C) Cells were grown in a non-permissive condition for 1, 3 and 8 days, followed by colony counting. Escape frequencies increased gradually over time. All graphs represent the mean ± SD, with n = 3.