Absence of insertions among spontaneous mutants of Salmonella typhimurium

Josep Casadesus, John R. Roth

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30 Scopus citations


While insertion sequences (IS) in Escherichia coli transpose frequently to generate spontaneous insertion mutants, such mutations are rare in Salmonella typhimurium: the only documented insertion mutation is a hisD mutation caused by the Salmonella-specific IS element IS 200. To obtain more examples of IS 200 insertion mutations and to seek additional types of IS elements in Salmonella, we selected and characterized 422 independent, spontaneous His- mutants and some 2100 additional mutants that are not necessarily independent. None of the mutants showed the absolute polar effect characteristic of insertion mutations or the reversion properties characteristic of insertions (low spontaneous reversion frequency and no reversion induction by chemical mutagens). A few mutants, showing a high spontaneous reversion frequency, were screened physically. No insertion mutations were found. Thus insertion mutations appear to be rare in S. typhimurium, in strong contrast to E. coli and despite the possession in Salmonella of at least one type of insertion element (IS 200). These results suggest that in Salmonella transposition of the endogenous elements has been controlled. The transposition ability of the elements may have been reduced or favored target sites removed from the host genome.

Original languageEnglish (US)
Pages (from-to)210-216
Number of pages7
JournalMGG Molecular & General Genetics
Issue number2-3
StatePublished - Apr 1989
Externally publishedYes


  • Histidine auxotrophs
  • Polar mutations
  • Salt sensitivity

ASJC Scopus subject areas

  • Genetics


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