Genome Evolution in the Salmonellae

The genus Salmonella, composed of many species that occupy different habitats, diverged from Escherichia over 100 million years ago (see also Chapter 17). S. typhimurium LT2 has been studied genetically for many years. We have used four major methods to collect data from pulsed-field gel electrophoresis (see Chapters 24–26) on the structure of the genome of several species of Salmonella: 1) The endonuclease I-CeuI to determine an rrn operon skeleton; 2) Tn10s, which are inserted in specific genes for transduction into new species, and physical mapping of the genes; 3) Double digestion following excision of fragments in agarose; 4) Mud-P22s (see also Chapter 27) as linking probes.