Kin discrimination promotes horizontal gene transfer between unrelated strains inBacillus subtilis

B. subtilis is a surface-dwelling bacterium that is competent for natural transformation. Genetically distinct B. subtilis swarms form a boundary upon encounter, mediated by a fast-evolving molecular kin discrimination (KD) system. We here demonstrate that KD-mediated swarm antagonisms in B. subtilis promote transformation-mediated horizontal gene transfer between strains of low relatedness. Gene transfer is largely uni-directional and the result of the induction of competence of the recipient strain by the donor strain is linked to a sigW-mediated stress response. More closely related strains, which in theory would experience more efficient recombination due to increased sequence homology, did not upregulate transformation upon encounter, demonstrating that social interactions can override mechanistic barriers to horizontal gene transfer. KD-mediated competence in response to the encounter of distinct neighbouring strains could maximize the probability of efficient incorporation of novel alleles and genes that have proved to function in a genomically and ecologically similar context.