title: Improving Salmonella vector with rec mutation to stabilize the DNA cargoes.
abstract: BACKGROUND
  Salmonella has been employed to deliver therapeutic molecules against cancer and infectious diseases. As the carrier for target gene(s), the cargo plasmid should be stable in the bacterial vector. Plasmid recombination has been reduced in E. coli by mutating several genes including the recA, recE, recF and recJ. However, to our knowledge, there have been no published studies of the effect of these or any other genes that play a role in plasmid recombination in Salmonella enterica.
  
  
  RESULTS
  The effect of recA, recF and recJ deletions on DNA recombination was examined in three serotypes of Salmonella enterica. We found that (1) intraplasmid recombination between direct duplications was RecF-independent in Typhimurium and Paratyphi A, but could be significantly reduced in Typhi by a ΔrecA or ΔrecF mutation; (2) in all three Salmonella serotypes, both ΔrecA and ΔrecF mutations reduced intraplasmid recombination when a 1041 bp intervening sequence was present between the duplications; (3) ΔrecA and ΔrecF mutations resulted in lower frequencies of interplasmid recombination in Typhimurium and Paratyphi A, but not in Typhi; (4) in some cases, a ΔrecJ mutation could reduce plasmid recombination but was less effective than ΔrecA and ΔrecF mutations. We also examined chromosome-related recombination. The frequencies of intrachromosomal recombination and plasmid integration into the chromosome were 2 and 3 logs lower than plasmid recombination frequencies in Rec+ strains. A ΔrecA mutation reduced both intrachromosomal recombination and plasmid integration frequencies.
  
  
  CONCLUSIONS
  The ΔrecA and ΔrecF mutations can reduce plasmid recombination frequencies in Salmonella enterica, but the effect can vary between serovars. This information will be useful for developing Salmonella delivery vectors able to stably maintain plasmid cargoes for vaccine development and gene therapy.
authors.affiliation: The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: Xiangmin
authors.initials: X
authors.lastname: Zhang
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Wanda
authors.forename: Karen
authors.initials: K
authors.lastname: Brenneman
authors.forename: Wei
authors.initials: W
authors.lastname: Kong
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Kenneth
authors.initials: K
authors.lastname: Roland
authors.forename: Roy
authors.initials: R
authors.lastname: Curtiss
mesh_terms: D000818:Animals; D004926:Escherichia coli / Q000235:genetics; D005822:Genetic Vectors; D051379:Mice; D008807:Mice, Inbred BALB C; D010957:Plasmids / Q000235:genetics*; D011938:Rec A Recombinases / Q000235:genetics; D011995:Recombination, Genetic; D019779:Salmonella enterica / Q000235:genetics*; D017384:Sequence Deletion
chemical_list: D011938:Rec A Recombinases