title: A genome-wide study of recombination rate variation in Bartonella henselae.
abstract: BACKGROUND
  Rates of recombination vary by three orders of magnitude in bacteria but the reasons for this variation is unclear. We performed a genome-wide study of recombination rate variation among genes in the intracellular bacterium Bartonella henselae, which has among the lowest estimated ratio of recombination relative to mutation in prokaryotes.
  
  
  RESULTS
  The 1.9 Mb genomes of B. henselae strains IC11, UGA10 and Houston-1 genomes showed only minor gene content variation. Nucleotide sequence divergence levels were less than 1% and the relative rate of recombination to mutation was estimated to 1.1 for the genome overall. Four to eight segments per genome presented significantly enhanced divergences, the most pronounced of which were the virB and trw gene clusters for type IV secretion systems that play essential roles in the infection process. Consistently, multiple recombination events were identified inside these gene clusters. High recombination frequencies were also observed for a gene putatively involved in iron metabolism. A phylogenetic study of this gene in 80 strains of Bartonella quintana, B. henselae and B. grahamii indicated different population structures for each species and revealed horizontal gene transfers across Bartonella species with different host preferences.
  
  
  CONCLUSIONS
  Our analysis has shown little novel gene acquisition in B. henselae, indicative of a closed pan-genome, but higher recombination frequencies within the population than previously estimated. We propose that the dramatically increased fixation rate for recombination events at gene clusters for type IV secretion systems is driven by selection for sequence variability.
authors.affiliation: Department of Molecular Evolution, Biomedical Centre, Uppsala University, SE-751 24, Uppsala, Sweden.
authors.forename: Lionel
authors.initials: L
authors.lastname: Guy
authors.forename: Björn
authors.initials: B
authors.lastname: Nystedt
authors.forename: Yu
authors.initials: Y
authors.lastname: Sun
authors.forename: Kristina
authors.initials: K
authors.lastname: Näslund
authors.forename: Eva C
authors.initials: EC
authors.lastname: Berglund
authors.forename: Siv G E
authors.initials: SG
authors.lastname: Andersson
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics; D018416:Bartonella henselae / Q000235:genetics*; D055028:Comparative Genomic Hybridization; D004269:DNA, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D005810:Multigene Family; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA
chemical_list: D058947:Bacterial Secretion Systems; D004269:DNA, Bacterial