title: Transposition of the heat-stable toxin astA gene into a gifsy-2-related prophage of Salmonella enterica serovar Abortusovis.
abstract: The horizontal transfer and acquisition of virulence genes via mobile genetic elements have been a major driving force in the evolution of Salmonella pathogenicity. Serovars of Salmonella enterica carry variable assortments of phage-encoded virulence genes, suggesting that temperate phages play a pivotal role in this process. Epidemic isolates of S. enterica serovar Typhimurium are consistently lysogenic for two lambdoid phages, Gifsy-1 and Gifsy-2, carrying known virulence genes. Other serovars of S. enterica, including serovars Dublin, Gallinarum, Enteritidis, and Hadar, carry distinct prophages with similarity to the Gifsy phages. In this study, we analyzed Gifsy-related loci from S. enterica serovar Abortusovis, a pathogen associated exclusively with ovine infection. A cryptic prophage, closely related to serovar Typhimurium phage Gifsy-2, was identified. This element, named Gifsy-2AO, was shown to contribute to serovar Abortusovis systemic infection in lambs. Sequence analysis of the prophage b region showed a large deletion which covers genes encoding phage tail fiber proteins and putative virulence factors, including type III secreted effector protein SseI (GtgB, SrfH). This deletion was identified in most of the serovar Abortusovis isolates tested and might be dependent on the replicative transposition of an adjacent insertion sequence, IS1414, previously identified in pathogenic Escherichia coli strains. IS1414 encodes heat-stable toxin EAST1 (astA) and showed multiple genomic copies in isolates of serovar Abortusovis. To our knowledge, this is the first evidence of intergeneric transfer of virulence genes via insertion sequence elements in Salmonella. The acquisition of IS1414 (EAST1) and its frequent transposition within the chromosome might improve the fitness of serovar Abortusovis within its narrow ecological niche.
authors.affiliation: Department of Biomedical Sciences, Center for Biotechnology Development and Biodiversity Research, University of Sassari, Italy.
authors.forename: Donatella
authors.initials: D
authors.lastname: Bacciu
authors.forename: Giovanni
authors.initials: G
authors.lastname: Falchi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Spazziani
authors.forename: Lionello
authors.initials: L
authors.lastname: Bossi
authors.forename: Gavino
authors.initials: G
authors.lastname: Marogna
authors.forename: Guido Sisinnio
authors.initials: GS
authors.lastname: Leori
authors.forename: Salvatore
authors.initials: S
authors.lastname: Rubino
authors.forename: Sergio
authors.initials: S
authors.lastname: Uzzau
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics*; D015169:Colony Count, Microbial; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D018628:Gene Dosage; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D005814:Genes, Viral; D007422:Intestines / Q000382:microbiology; D008099:Liver / Q000382:microbiology; D008198:Lymph Nodes / Q000382:microbiology; D008969:Molecular Sequence Data; D039002:Prophages / Q000235:genetics* / Q000302:isolation & purification; D012481:Salmonella Infections, Animal / Q000382:microbiology; D019779:Salmonella enterica / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity / Q000821:virology*; D012757:Sheep Diseases / Q000382:microbiology; D013154:Spleen / Q000382:microbiology; D017376:Viral Tail Proteins / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D017376:Viral Tail Proteins; D037521:Virulence Factors