Phage-based microbiome manipulation elucidates interactions within community context

Testing microbial interaction hypotheses remains a major challenge in microbiome research. Bacteriophages have the potential to probe organism-organism interactions within complex microbiomes, yet are rarely used for this purpose. Here, we isolated nine narrow host range phages that replicate in several ecologically important Variovorax species. As Variovorax CL14 degrades the plant root-stunting hormone auxin, we used phages to eliminate V. CL14 from a rhizosphere consortium and reestablished the stunted root phenotype. We used three of the phages to deplete another Variovorax , SCN45, from complex communities to test correlation network-based hypotheses of thiamine interdependencies. Genome-resolved metagenomics revealed that specific taxa decreased in relative abundance following Variovorax depletion and could be rescued by thiamine supplementation. Thus, we confirmed thiamine production as the mechanistic basis for interdependence. These experiments lay the foundation for research that employs wildtype and engineered phages to test interaction hypotheses and for targeted microbiome manipulation.