title: Plasmid selection in Escherichia coli using an endogenous essential gene marker.
abstract: BACKGROUND
  Antibiotic resistance genes are widely used for selection of recombinant bacteria, but their use risks contributing to the spread of antibiotic resistance. In particular, the practice is inappropriate for some intrinsically resistant bacteria and in vaccine production, and costly for industrial scale production. Non-antibiotic systems are available, but require mutant host strains, defined media or expensive reagents. An unexplored concept is over-expression of a host essential gene to enable selection in the presence of a chemical inhibitor of the gene product. To test this idea in E. coli, we used the growth essential target gene fabI as the plasmid-borne marker and the biocide triclosan as the selective agent.
  
  
  RESULTS
  The new cloning vector, pFab, enabled selection by triclosan at 1 microM. Interestingly, pFab out-performed the parent pUC19-ampicillin system in cell growth, plasmid stability and plasmid yield. Also, pFab was toxic to host cells in a way that was reversed by triclosan. Therefore, pFab and triclosan are toxic when used alone but in combination they enhance growth and plasmid production through a gene-inhibitor interaction.
  
  
  CONCLUSIONS
  The fabI-triclosan model system provides an alternative plasmid selection method based on essential gene over-expression, without the use of antibiotic-resistance genes and conventional antibiotics.
authors.affiliation: Department of Cell and Molecular Biology, Karolinska Institute, Stockholm, SE-17177, Sweden. shan.goh@ki.se
authors.forename: Shan
authors.initials: S
authors.lastname: Goh
authors.forename: Liam
authors.initials: L
authors.lastname: Good
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH) / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000235:genetics*; D054889:Fatty Acid Synthase, Type II; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005798:Genes, Bacterial; D020043:Genes, Essential; D005822:Genetic Vectors; D050296:Microbial Viability; D010957:Plasmids; D012641:Selection, Genetic; D014169:Transformation, Bacterial; D014260:Triclosan / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D014260:Triclosan; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH); C493924:fabI protein, E coli; D054889:Fatty Acid Synthase, Type II