Genetic mapping by duplication segregation in Salmonella enterica

MudP and MudQ elements were used to induce duplications in Salmonella enter ica 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 favorabl e trait for duplication formation, probably because homology length is a li miting factor for the central crossover. Additional requirements are a mult iplicity of infection of 2 or higher in the infecting phage suspensions (wh ich reflects the need of two transduced fragments) and an exponentially gro wing recipient (which reflects the need of a chromosome replication fork). We describe a set of II 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 tr ansposon insertion in or near the locus to be mapped) is transduced into th e 11-strain set. Several transductants from each cross are grown nonselecti vely, and haploid segregants are scored for the presence of the marker. If all the segregants contain the transduced marker, it maps outside the dupli cation interval. If the marker is found only in a fraction of the segregant s, it maps within the duplicated region.