Genetic mapping by duplication segregation in Salmonella enterica.

MudP and MudQ elements were used to induce duplications in Salmonella enterica by formation of a triple crossover between two transduced fragments and the host chromosome. The large size (36 kb) of MudP and MudQ is a favorable trait for duplication formation, probably because homology length is a limiting factor for the central crossover. Additional requirements are a multiplicity of infection of 2 or higher in the infecting phage suspensions (which reflects the need of two transduced fragments) and an exponentially growing recipient (which reflects the need of a chromosome replication fork). We describe a set of 11 strains of S. enterica, each carrying a chromosomal duplication with known endpoints. The collection covers all the Salmonella chromosome except the terminus. For mapping, a dominant marker (e.g., a transposon insertion in or near the locus to be mapped) is transduced into the 11-strain set. Several transductants from each cross are grown nonselectively, and haploid segregants are scored for the presence of the marker. If all the segregants contain the transduced marker, it maps outside the duplication interval. If the marker is found only in a fraction of the segregants, it maps within the duplicated region.