Microbial selection drives adaptation Many legumes have a host-symbiote relationship with nitrogen-fixing bacteria, or rhizobia, that provides a benefit to both the plant and the microbe. Batstone et al. experimentally evolved the association between five legume accessions and different bacterial isolates. Rather than observe selection by the host for bacterial associations (host choice), mutations accumulated within a bacterial plasmid and increased the strength of the mutualism. Thus, local and recent associations between bacterial strains and plant genotypes are due to selection for bacterial adaptation. Science, this issue p. 476 The evolution of bacteria–plant associations involves adaptation of the bacteria rather than host choice. Advances in microbiome science require a better understanding of how beneficial microbes adapt to hosts. We tested whether hosts select for more-cooperative microbial strains with a year-long evolution experiment and a cross-inoculation experiment designed to explore how nitrogen-fixing bacteria (rhizobia) adapt to legumes. We paired the bacterium Ensifer meliloti with one of five Medicago truncatula genotypes that vary in how strongly they “choose” bacterial symbionts. Independent of host choice, E. meliloti rapidly adapted to its local host genotype, and derived microbes were more beneficial when they shared evolutionary history with their host. This local adaptation was mostly limited to the symbiosis plasmids, with mutations in putative signaling genes. Thus, cooperation depends on the match between partner genotypes and increases as bacteria adapt to their local host.

中文翻译：

---

实验进化使微生物与其本地宿主基因型更加合作

微生物选择驱动适应 许多豆类与固氮细菌或根瘤菌存在宿主共生关系，这对植物和微生物都有益。巴特斯通等人。实验进化了五种豆科植物种质与不同细菌分离株之间的关联。与其观察宿主对细菌关联的选择（宿主选择），不如在细菌质粒中积累突变并增加共生的强度。因此，细菌菌株和植物基因型之间的局部和近期关联是由于细菌适应的选择。科学，这个问题 p。476 细菌-植物关联的进化涉及细菌的适应而不是宿主选择。微生物组科学的进步需要更好地了解有益微生物如何适应宿主。我们通过为期一年的进化实验和旨在探索固氮细菌（根瘤菌）如何适应豆类的交叉接种实验，测试宿主是否选择更合作的微生物菌株。我们将细菌 Ensifer meliloti 与五种苜蓿基因型中的一种配对，这些基因型在“选择”细菌共生体的强度方面各不相同。独立于宿主选择，E. meliloti 迅速适应其本地宿主基因型，当衍生微生物与宿主共享进化历史时，它们更有益。这种局部适应主要限于共生质粒，假定信号基因发生突变。因此，合作取决于伙伴基因型之间的匹配，并且随着细菌适应其本地宿主而增加。