Swarming is the collective movement of bacteria across a surface. It requires the production of surfactants (public goods) to overcome surface tension and provides an excellent model to investigate bacterial cooperation. Previously, we correlated swarm interaction phenotypes with kin discrimination between B. subtilis soil isolates, by showing that less related strains form boundaries between swarms and highly related strains merge. However, how kin discrimination affects cooperation and territoriality in swarming bacteria remains little explored. Here we show that the pattern of surface colonization by swarming mixtures is influenced by kin types. Closely related strain mixtures colonize the surface in a mixed swarm, while mixtures of less related strains show competitive exclusion as only one strain colonizes the surface. The outcome of nonkin swarm expansion depends on the initial ratio of the competing strains, indicating positive frequency-dependent competition. We find that addition of surfactin (a public good excreted from cells) can complement the swarming defect of nonkin mutants, whereas close encounters in nonkin mixtures lead to territorial exclusion, which limits the exploitation of surfactin by nonkin nonproducers. The work suggests that kin discrimination driven competitive territorial exclusion may be an important determinant for the success of cooperative surface colonization.

蜂群是细菌在表面上的集体运动。它需要生产表面活性剂（公共产品）来克服表面张力，并为研究细菌合作提供了一个很好的模型。以前，我们将群体相互作用表型与B. subtilis之间的亲缘歧视相关联土壤分离株，通过显示相关性较低的菌株在群体和高度相关的菌株之间形成边界合并。然而，亲属歧视如何影响集群细菌的合作和领地性仍鲜有探索。在这里，我们表明蜂群混合物在表面定植的模式受亲属类型的影响。密切相关的菌株混合物在混合群中定植于表面，而相关性较低的菌株的混合物显示出竞争排斥，因为只有一种菌株在表面定殖。nonkin 群体扩张的结果取决于竞争菌株的初始比率，表明积极的频率依赖竞争。我们发现添加 surfactin（一种从细胞中排出的公共物品）可以弥补 nonkin 突变体的蜂群缺陷，而在非亲属混合物中的近距离接触会导致领土排斥，这限制了非亲属非生产者对表面活性素的利用。这项工作表明，亲属歧视驱动的竞争性领土排斥可能是合作表面殖民成功的重要决定因素。