MudSacI, a transposon with strong selectable and counterselectable markers: use for rapid mapping of chromosomal mutations in Salmonella typhimurium

The transposable bacteriophage Mu and its mini-Mu derivatives are useful tools for the genetic analysis of many bacteria. A variety of antibiotic-resistant Mu derivatives have been constructed, allowing direct selection for cells which contain the transposon. However, in many cases a counterselection against the transposon would greatly facilitate further genetic analysis. In this paper we report the construction of MudSacI, a mini-Mu derived transposon containing the sacB (secretory levansucrase) gene of Bacillus subtilis, which confers sucrose sensitivity upon gram-negative bacteria. We describe the use of this transposon as a tool for rapid genetic mapping of chromosomal genes in Salmonella typhimurium. Simple modifications of this approach should facilitate rapid mapping in many other bacteria as well.