Salmonella Paratyphi C: Genetic Divergence From Salmonella Choleraesuis and Pathogenic Convergence With Salmonella Typhi

PLoS One. 2009;4(2):e4510. doi: 10.1371/journal.pone.0004510. Epub 2009 Feb 20.

Abstract

Background: Although over 1400 Salmonella serovars cause usually self-limited gastroenteritis in humans, a few, e.g., Salmonella typhi and S. paratyphi C, cause typhoid, a potentially fatal systemic infection. It is not known whether the typhoid agents have evolved from a common ancestor (by divergent processes) or acquired similar pathogenic traits independently (by convergent processes). Comparison of different typhoid agents with non-typhoidal Salmonella lineages will provide excellent models for studies on how similar pathogens might have evolved.

Methodologies/principal findings: We sequenced a strain of S. paratyphi C, RKS4594, and compared it with previously sequenced Salmonella strains. RKS4594 contains a chromosome of 4,833,080 bp and a plasmid of 55,414 bp. We predicted 4,640 intact coding sequences (4,578 in the chromosome and 62 in the plasmid) and 152 pseudogenes (149 in the chromosome and 3 in the plasmid). RKS4594 shares as many as 4346 of the 4,640 genes with a strain of S. choleraesuis, which is primarily a swine pathogen, but only 4008 genes with another human-adapted typhoid agent, S. typhi. Comparison of 3691 genes shared by all six sequenced Salmonella strains placed S. paratyphi C and S. choleraesuis together at one end, and S. typhi at the opposite end, of the phylogenetic tree, demonstrating separate ancestries of the human-adapted typhoid agents. S. paratyphi C seemed to have suffered enormous selection pressures during its adaptation to man as suggested by the differential nucleotide substitutions and different sets of pseudogenes, between S. paratyphi C and S. choleraesuis.

Conclusions: S. paratyphi C does not share a common ancestor with other human-adapted typhoid agents, supporting the convergent evolution model of the typhoid agents. S. paratyphi C has diverged from a common ancestor with S. choleraesuis by accumulating genomic novelty during adaptation to man.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Genes, Bacterial / genetics*
  • Genome, Bacterial*
  • Humans
  • Phylogeny*
  • Salmonella / genetics*
  • Salmonella arizonae / genetics
  • Salmonella paratyphi C / genetics
  • Salmonella typhi / genetics
  • Selection, Genetic
  • Sequence Analysis, DNA
  • Species Specificity
  • Swine