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Table 2 Escape frequencies of selected biosafety systems

From: Auxotrophy to Xeno-DNA: an exploration of combinatorial mechanisms for a high-fidelity biosafety system for synthetic biology applications

Name of the System Type of System Escape Frequency Reference
SLiDE, single allele Auxotrophy 8 × 10− 4 to 3 × 10− 9 [69]
SLiDE, two alleles Auxotrophy 5 × 10− 10 [69]
SLiDE, three alleles Auxotrophy < 3 × 10− 11 [69]
Thymine/Thymidine auxotrophy Auxotrophy Below detection limit [71, 72]
Artificial Phosphite Dependency Auxotrophy 1.94 × 10− 13 [70]
Single ncAA auxotrophy Auxotrophy/Xenobiology No escape mutants in >5 × 1011 cells [381]
Triple ncAA auxotrophy Auxotrophy/Xenobiology 6.41 × 10−11 [57]
CcdB Kill switch ~ 10− 3 [28]
Cryodeath Kill switch < 1 in 105 after 10 days in vivo [107]
Deadman Kill switch Below detection limit [28]
Passcode Kill switch Below detection limit [28]
CRISPR mediated DNA degradation DNA destruction Viable cells reduced by a factor of 108 [152]
Thermoinduced DNA degradation DNA destruction 2 × 10–5 [135]
GeneGuard Combinatorial system Below detection limit [32]
SafeGuard Combinatorial system <1.3 × 10− 12 [76]
  1. In general, the combination of several systems reduces the probability for random mutagenesis to disarm the biosafety system and for cells to bypass the biosafety system. Therefore, multilayered systems like Passcode, Deadman or GeneGuard act as great examples for complex biosafety systems that achieved very low escape frequencies. Engineering artificial auxotrophies, such as an artificial phosphite dependency, can also act as potent biosafety systems, as shown by Hirota et al.