title: A barrier to homologous recombination between sympatric strains of the cooperative soil bacterium Myxococcus xanthus.
abstract: The bacterium Myxococcus xanthus glides through soil in search of prey microbes, but when food sources run out, cells cooperatively construct and sporulate within multicellular fruiting bodies. M. xanthus strains isolated from a 16 × 16-cm-scale patch of soil were previously shown to have diversified into many distinct compatibility types that are distinguished by the failure of swarming colonies to merge upon encounter. We sequenced the genomes of 22 isolates from this population belonging to the two most frequently occurring multilocus sequence type (MLST) clades to trace patterns of incipient genomic divergence, specifically related to social divergence. Although homologous recombination occurs frequently within the two MLST clades, we find an almost complete absence of recombination events between them. As the two clades are very closely related and live in sympatry, either ecological or genetic barriers must reduce genetic exchange between them. We find that the rate of change in the accessory genome is greater than the rate of amino-acid substitution in the core genome. We identify a large genomic tract that consistently differs between isolates that do not freely merge and therefore is a candidate region for harbouring gene(s) responsible for self/non-self discrimination.
authors.affiliation: Department of Environmental Systems Science, Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wielgoss
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
authors.forename: Xavier
authors.initials: X
authors.lastname: Didelot
authors.affiliation: Centre for Genomic Research, University of Liverpool, Liverpool, UK.|Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
authors.forename: Roy R
authors.initials: RR
authors.lastname: Chaudhuri
authors.affiliation: Centre for Genomic Research, University of Liverpool, Liverpool, UK.
authors.forename: Xuan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Centre for Genomic Research, University of Liverpool, Liverpool, UK.|Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK.
authors.forename: Gareth D
authors.initials: GD
authors.lastname: Weedall
authors.affiliation: Department of Environmental Systems Science, Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Velicer
authors.affiliation: European Centre for Environmental and Human Health, Medical School, University of Exeter, Penryn, UK.
authors.forename: Michiel
authors.initials: M
authors.lastname: Vos
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D059765:Homologous Recombination; D058885:Multilocus Sequence Typing; D009154:Mutation; D016941:Myxococcus xanthus / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism; D010641:Phenotype; D012988:Soil Microbiology; D013171:Spores, Bacterial / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins