The genome of Salmonella enterica serovar gallinarum: distinct insertions/deletions and rare rearrangements.

Salmonella enterica serovar Gallinarum is a fowl-adapted pathogen, causing typhoid fever in chickens. It has the same antigenic formula (1,9,12:--:--) as S. enterica serovar Pullorum, which is also adapted to fowl but causes pullorum disease (diarrhea). The close relatedness but distinct pathogeneses make this pair of fowl pathogens good models for studies of bacterial genomic evolution and the way these organisms acquired pathogenicity. To locate and characterize the genomic differences between serovar Gallinarum and other salmonellae, we constructed a physical map of serovar Gallinarum strain SARB21 by using I-CeuI, XbaI, and AvrII with pulsed-field gel electrophoresis techniques. In the 4,740-kb genome, we located two insertions and six deletions relative to the genome of S. enterica serovar Typhimurium LT2, which we used as a reference Salmonella genome. Four of the genomic regions with reduced lengths corresponded to the four prophages in the genome of serovar Typhimurium LT2, and the others contained several smaller deletions relative to serovar Typhimurium LT2, including regions containing srfJ, std, and stj and gene clusters encoding a type I restriction system in serovar Typhimurium LT2. The map also revealed some rare rearrangements, including two inversions and several translocations. Further characterization of these insertions, deletions, and rearrangements will provide new insights into the molecular basis for the specific host-pathogen interactions and mechanisms of genomic evolution to create a new pathogen.