The complete sequence and analysis of the large virulence plasmid pSS of Shigella sonnei

Plasmid. 2005 Sep;54(2):149-59. doi: 10.1016/j.plasmid.2005.03.002. Epub 2005 Apr 20.


The complete sequence of pSS, which is the large virulence plasmid of Shigella sonnei, was determined. The 214-kb plasmid is composed of segments of virulence-associated genes, the O-antigen gene clusters, a range of replication and maintenance genes, and large numbers of insertion sequence (IS) elements. Two hundred and forty-one open reading frames (ORFs) were identified, of which 117 are highly homologous to IS elements or transposases, 57 are homologous to known pathogenesis-associated proteins, and 30 are related to replication, plasmid maintenance, or other metabolic functions. Thirty-seven ORFs have no similarity to proteins with a known function, including two with no significant similarity to any hypothetical proteins. Interestingly, 10 ORFs encoding O-antigen gene clusters were identified on the plasmid and this is markedly different from most other Shigella spp. virulent plasmids. A novel toxin-antitoxin system, a series of stbDE homologs, was found on the plasmid immediately downstream of the replication region; the sole segregation stability system may be responsible for the instability of pSS. The pSS plasmid is a mixture of genes with different origins and functions. The sequence suggests a remarkable history of IS-mediated recombination and acquisition of DNA across a range of bacterial species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Base Composition
  • DNA Primase
  • DNA Replication / genetics
  • DNA-Directed RNA Polymerases / genetics
  • Endodeoxyribonucleases / genetics
  • Escherichia coli Proteins / genetics
  • Exodeoxyribonucleases / genetics
  • Gene Transfer, Horizontal
  • Molecular Sequence Data
  • Multigene Family
  • O Antigens / genetics
  • Open Reading Frames
  • Plasmids / genetics*
  • Sequence Analysis
  • Shigella sonnei / genetics
  • Shigella sonnei / pathogenicity*
  • Virulence / genetics


  • Bacterial Proteins
  • Escherichia coli Proteins
  • O Antigens
  • chromosome partition proteins, bacterial
  • DNA Primase
  • DNA-Directed RNA Polymerases
  • Endodeoxyribonucleases
  • Exodeoxyribonucleases
  • dnaG protein, E coli

Associated data

  • GENBANK/CP000039