Pherotype polymorphism in Streptococcus pneumoniae has no obvious effects on population structure and recombination

Miller, Eric, Evans, Benjamin A ORCID:, Cornejo, Omar E, Roberts, Ian S and Rozen, Daniel E (2017) Pherotype polymorphism in Streptococcus pneumoniae has no obvious effects on population structure and recombination. Genome Biology and Evolution, 9 (10). 2546–2559. ISSN 1759-6653

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Natural transformation in the Gram-positive pathogen Streptococcus pneumoniae occurs when cells become “competent”, a state that is induced in response to high extracellular concentrations of a secreted peptide signal called CSP (Competence Stimulating Peptide) encoded by the comC locus. Two main CSP signal types (pherotypes) are known to dominate the pherotype diversity across strains. Using 4,089 fully sequenced pneumococcal genomes, we confirm that pneumococcal populations are highly genetically structured and that there is significant variation among diverged populations in pherotype frequencies; most carry only a single pherotype. Moreover, we find that the relative frequencies of the two dominant pherotypes significantly vary within a small range across geographical sites. It has been variously proposed that pherotypes either promote genetic exchange among cells expressing the same pherotype, or conversely that they promote recombination between strains bearing different pherotypes. We attempt to distinguish these hypotheses using a bioinformatics approach by estimating recombination frequencies within and between pherotypes across 4,089 full genomes. Despite underlying population structure, we observe extensive recombination between populations; additionally, we found significantly higher (although marginal) rates of genetic exchange between strains expressing different pherotypes than among isolates carrying the same pherotype. Our results indicate that pherotypes do not restrict, and may even slightly facilitate, recombination between strains; however, these marginal effects suggest the more likely possibility that the cause of CSP polymorphism lies outside of its effects on transformation. Our results suggest that the CSP balanced polymorphism does not causally underlie population differentiation. Therefore, when strains carrying different pherotypes encounter one another during co-colonization, genetic exchange can occur without restriction.

Item Type: Article
Uncontrolled Keywords: competence,pneumococcus,quorum sensing,balanced polymorphism,horizontal gene transfer
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
UEA Research Groups: Faculty of Medicine and Health Sciences > Research Groups > Gastroenterology and Gut Biology
Faculty of Medicine and Health Sciences > Research Centres > Metabolic Health
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Depositing User: Pure Connector
Date Deposited: 22 Sep 2017 05:06
Last Modified: 19 Oct 2023 02:04
DOI: 10.1093/gbe/evx188

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