title: Pherotypes are driving genetic differentiation within Streptococcus pneumoniae.
abstract: BACKGROUND
  The boundaries of bacterial species and the mechanisms underlying bacterial speciation are matters of intense debate. Theoretical studies have shown that recombination acts as a strong cohesive force preventing divergence in bacterial populations. Streptococcus pneumoniae populations have the telltale signs of high recombination with competence implicated as the major driving force behind gene exchange. Competence in S. pneumoniae is triggered by a quorum-sensing mechanism controlled by the competence-stimulating peptide pheromone.
  
  
  RESULTS
  We studied the distribution of the two major pherotypes in the pneumococcal population and their association with serotype, antimicrobial resistance and genetic lineage. Using multilocus sequence data we evaluated pherotype influence on the dynamics of horizontal gene transfer. We show that pherotype is a clonal property of pneumococci. Standard population genetic analysis and multilocus infinite allele model simulations support the hypothesis that two genetically differentiated populations are defined by the major pherotypes.
  
  
  CONCLUSIONS
  Severe limitations to gene flow can therefore occur in bacterial species in the absence of geographical barriers and within highly recombinogenic populations. This departure from panmixia can have important consequences for our understanding of the response of pneumococci to human imposed selective pressures such as vaccination and antibiotic use.
authors.affiliation: Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av, Prof, Egas Moniz, 1649-028 Lisboa, Portugal. mcarrolo@fm.ul.pt
authors.forename: Margarida
authors.initials: M
authors.lastname: Carrolo
authors.forename: Francisco R
authors.initials: FR
authors.lastname: Pinto
authors.forename: Jose
authors.initials: J
authors.lastname: Melo-Cristino
authors.forename: Mario
authors.initials: M
authors.lastname: Ramirez
mesh_terms: D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal; D005828:Genetics, Population; D008957:Models, Genetic; D053038:Quorum Sensing / Q000235:genetics; D013296:Streptococcus pneumoniae / Q000145:classification / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial