Tn1725 transposon mutagenesis of 9-18 delta 7, an EcoRI deletion derivative of Salmonella dublin lane plasmid pSDL2.

A 37.5-kb derivative of the Salmonella dublin virulence plasmid pSDL2 was subjected to mutagenesis with the transposon Tn1725. Fifty-two insertions were mapped, and the mutants were tested for their ability to restore virulence to a plasmid-free strain of S. dublin. Twenty-nine of these inserts could not restore full virulence and thus define nine regions of the plasmid essential for virulence. Deletion of a 4.5-kb region by Bal31 nuclease resulted in a 33-kb derivative that maintained full virulence.