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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][1] [1]: /lookup/doi/10.1126/science.abb7222