The Plant Host Induces Antibiotic Production To Select the Most-Beneficial Colonizers.

Microbial ecosystems tightly associated with a eukaryotic host are widespread in nature. The genetic and metabolic networks of the eukaryotic hosts and the associated microbes have coevolved to form a symbiotic relationship. Both the Gram-positive and the Gram-negative can form biofilms on plant roots and thus can serve as a model system for the study of interspecies interactions in a host-associated ecosystem. We found that biofilms expand collectively and asymmetrically toward , while expressing a nonribosomal antibiotic bacillaene and an extracellular protease. As a result, biofilms outcompeted for successful colonization of the host. Strikingly, the plant host was able to enhance the efficiency of this killing by inducing bacillaene synthesis. In turn, biofilms increased the resistance of the plant host to pathogens. These results provide an example of how plant-bacterium symbiosis promotes the immune response of the plant host and the fitness of the associated bacteria. Our study sheds mechanistic light on how multicellular biofilm units compete to successfully colonize a eukaryote host, using microbial communities as our lens. The microbiota and its interactions with its host play various roles in the development and prevention of diseases. Using competing beneficial biofilms that are essential microbiota members on the plant host, we found that biofilms activate collective migration to capture their prey, followed by nonribosomal antibiotic synthesis. Plant hosts increase the efficiency of antibiotic production by biofilms, as they activate the synthesis of polyketides; therefore, our study provides evidence of a mechanism by which the host can indirectly select for beneficial microbiota members.