Team:Hong Kong HKU/safety



Question: Will mobile DNA elements create a superbug?

Answer: Interestingly, mobile DNA elements are used by pathogens and microbes to develop virulence, resistance as well as phenotypic variations[1]. This will allow their survival in the presence of selective pressure like antibiotics, environmental variations and escape to nutrient-rich areas.

Wild type Cre may cause gene shuffling by binding to nonspecific DNA target sites. Which causes genes to shuffle and hence may increase genetic diversity. These mechanisms are very abundant in natural populations via natural invertases [2], strand breakage mediated strand transversion via the collision of DNA and RNA polymerases [3], and replication errors [4]. And shuffling off-site due to wild type Cre indeed adds variation in a population. However, without selective pressure, microevolution still has slow progress.

Moreover, we would be using mutant versions of Cre[5], which introduces another layer of off-target stability and specificity. With an additional kill switch, we would be able to prevent cross-reaction of loxP with off-target sites, and also screen out deletion mutants.


  1. Bonifield HR, Hughes KT. Flagellar phase variation in Salmonella enterica is mediated by a posttranscriptional control mechanism. Journal of bacteriology. 2003 Jun 15;185(12):3567-74.
  2. Boyce KJ, Wang Y, Verma S, Shakya VP, Xue C, Idnurm A. Mismatch repair of DNA replication errors contributes to microevolution in the pathogenic fungus Cryptococcus neoformans. MBio. 2017 Jul 5;8(3).
  3. Ene IV, Farrer RA, Hirakawa MP, Agwamba K, Cuomo CA, Bennett RJ. Global analysis of mutations driving microevolution of a heterozygous diploid fungal pathogen. Proceedings of the National Academy of Sciences. 2018 Sep 11;115(37):E8688-97.
  4. Eroshenko N, Church GM. Mutants of Cre recombinase with improved accuracy. Nature communications. 2013 Sep 23;4(1):1-0.
  5. Ormerod KL, Morrow CA, Chow EW, Lee IR, Arras SD, Schirra HJ, Cox GM, Fries BC, Fraser JA. Comparative genomics of serial isolates of Cryptococcus neoformans reveals gene associated with carbon utilization and virulence. G3: Genes, Genomes, Genetics. 2013 Apr 1;3(4):675-86.