Research article
Pherotypes are driving genetic differentiation within Streptococcus pneumoniae
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* Corresponding author: Mario Ramirez ramirez@fm.ul.pt
- † Equal contributors
1 Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisboa, Portugal
2 Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
BMC Microbiology 2009, 9:191 doi:10.1186/1471-2180-9-191
Published: 7 September 2009Abstract
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.
Conclusion
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.