Precise excision and secondary transposition of TnphoA in non-motile mutants of a Salmonella enterica serovar Enteritidis clinical isolate

Mutagenesis with TnphoA has been widely used in many bacteria. Here, we report the excision and secondary transposition of this transposon in three non-motile (fliC, fliF and motB) mutants of Salmonella enterica serovar Enteritidis (S. Enteritidis). Isolation of motile revertants showed that they were kanamycin resistant and conserved a copy of TnphoA in their genome in an insertion site different from the initial one. They also expressed an intact flagella. Characterization of the motile revertant derived from the fliC mutant showed that TnphoA excised precisely from the fliC gene, resulting in an equivalent amount of FliC secreted protein in the revertant compared to that of the wild-type strain. These results show that TnphoA mutants should be used with care and underline the value of using transposon derivatives lacking the transposase gene.