title: Analysis of evolutionary patterns of genes in Campylobacter jejuni and C. coli.
abstract: BACKGROUND
  The thermophilic Campylobacter jejuni and Campylobacter coli are considered weakly clonal populations where incongruences between genetic markers are assumed to be due to random horizontal transfer of genomic DNA. In order to investigate the population genetics structure we extracted a set of 1180 core gene families (CGF) from 27 sequenced genomes of C. jejuni and C. coli. We adopted a principal component analysis (PCA) on the normalized evolutionary distances in order to reveal any patterns in the evolutionary signals contained within the various CGFs.
  
  
  RESULTS
  The analysis indicates that the conserved genes in Campylobacter show at least two, possibly five, distinct patterns of evolutionary signals, seen as clusters in the score-space of our PCA. The dominant underlying factor separating the core genes is the ability to distinguish C. jejuni from C. coli. The genes in the clusters outside the main gene group have a strong tendency of being chromosomal neighbors, which is natural if they share a common evolutionary history. Also, the most distinct cluster outside the main group is enriched with genes under positive selection and displays larger than average recombination rates.
  
  
  CONCLUSIONS
  The Campylobacter genomes investigated here show that subsets of conserved genes differ from each other in a more systematic way than expected by random horizontal transfer, and is consistent with differences in selection pressure acting on different genes. These findings are indications of a population of bacteria characterized by genomes with a mixture of evolutionary patterns.
authors.affiliation: Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway. lars.snipen@umb.no.
authors.forename: Lars
authors.initials: L
authors.lastname: Snipen
authors.forename: Trudy M
authors.initials: TM
authors.lastname: Wassenaar
authors.forename: Eric
authors.initials: E
authors.lastname: Altermann
authors.forename: Jonathan
authors.initials: J
authors.lastname: Olson
authors.forename: Sophia
authors.initials: S
authors.lastname: Kathariou
authors.forename: Karin
authors.initials: K
authors.lastname: Lagesen
authors.forename: Monica
authors.initials: M
authors.lastname: Takamiya
authors.forename: Susanne
authors.initials: S
authors.lastname: Knøchel
authors.forename: David W
authors.initials: DW
authors.lastname: Ussery
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Meinersmann