title: Composition, acquisition, and distribution of the Vi exopolysaccharide-encoding Salmonella enterica pathogenicity island SPI-7.
abstract: Vi capsular polysaccharide production is encoded by the viaB locus, which has a limited distribution in Salmonella enterica serovars. In S. enterica serovar Typhi, viaB is encoded on a 134-kb pathogenicity island known as SPI-7 that is located between partially duplicated tRNA(pheU) sites. Functional and bioinformatic analysis suggests that SPI-7 has a mosaic structure and may have evolved as a consequence of several independent insertion events. Analysis of viaB-associated DNA in Vi-positive S. enterica serovar Paratyphi C and S. enterica serovar Dublin isolates revealed the presence of similar SPI-7 islands. In S. enterica serovars Paratyphi C and Dublin, the SopE bacteriophage and a 15-kb fragment adjacent to the intact tRNA(pheU) site were absent. In S. enterica serovar Paratyphi C only, a region encoding a type IV pilus involved in the adherence of S. enterica serovar Typhi to host cells was missing. The remainder of the SPI-7 islands investigated exhibited over 99% DNA sequence identity in the three serovars. Of 30 other Salmonella serovars examined, 24 contained no insertions at the equivalent tRNA(pheU) site, 2 had a 3.7-kb insertion, and 4 showed sequence variation at the tRNA(pheU)-phoN junction, which was not analyzed further. Sequence analysis of the SPI-7 region from S. enterica serovar Typhi strain CT18 revealed significant synteny with clusters of genes from a variety of saprophytic bacteria and phytobacteria, including Pseudomonas aeruginosa and Xanthomonas axonopodis pv. citri. This analysis suggested that SPI-7 may be a mobile element, such as a conjugative transposon or an integrated plasmid remnant.
authors.affiliation: Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, Armstrong Road, London SW7 2AZ, UK. d.pickard@imperial.ac.uk
authors.forename: Derek
authors.initials: D
authors.lastname: Pickard
authors.forename: John
authors.initials: J
authors.lastname: Wain
authors.forename: Stephen
authors.initials: S
authors.lastname: Baker
authors.forename: Alexandra
authors.initials: A
authors.lastname: Line
authors.forename: Sonia
authors.initials: S
authors.lastname: Chohan
authors.forename: Maria
authors.initials: M
authors.lastname: Fookes
authors.forename: Andrew
authors.initials: A
authors.lastname: Barron
authors.forename: Peadar O
authors.initials: PO
authors.lastname: Gaora
authors.forename: José A
authors.initials: JA
authors.lastname: Chabalgoity
authors.forename: Niren
authors.initials: N
authors.lastname: Thanky
authors.forename: Christoph
authors.initials: C
authors.lastname: Scholes
authors.forename: Nicholas
authors.initials: N
authors.lastname: Thomson
authors.forename: Michael
authors.initials: M
authors.lastname: Quail
authors.forename: Julian
authors.initials: J
authors.lastname: Parkhill
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D016971:Citrobacter freundii / Q000235:genetics; D019295:Computational Biology; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D010944:Plants / Q000382:microbiology; D011135:Polysaccharides, Bacterial / Q000235:genetics*; D012346:RNA, Transfer, Amino Acyl / Q000235:genetics; D019779:Salmonella enterica / Q000145:classification / Q000235:genetics / Q000472:pathogenicity*; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D011135:Polysaccharides, Bacterial; D012346:RNA, Transfer, Amino Acyl; C054154:capsular polysaccharide, Salmonella