Aarhus-Utrecht Study: Plants Recruit Root Bacteria by Function, Not Species

05 October 2026, Denmark: Plant roots do not select their bacterial partners by species, but by what those bacteria can actually do, according to a new study from Aarhus University in Denmark and Utrecht University in the Netherlands that the authors say offers a practical blueprint for designing better microbial biostimulants and biofertilizers.

The study was published in Nature Microbiology on September 17, 2026, led by senior authors Professor Simona Radutoiu of Aarhus University and Associate Professor Ronnie de Jonge of Utrecht University, with first author Gijs Selten of Utrecht University and co-author Florian Lamouche of Aarhus University. The collaboration also included researchers from the University of Copenhagen, INRAE Angers in France, and Friedrich Schiller University Jena in Germany.

The root microbiome, the community of bacteria and other microbes that colonize plant roots, is already known to help many crops take up nutrients, tolerate drought or other stress, and resist disease, which is why it has become a major focus for companies developing biological fertilizers and biostimulants. What has been less clear is exactly how a plant decides which bacteria, out of the vast and varied population present in soil, get to colonize its roots in the first place.

To answer that, the team analyzed nearly 1,000 bacterial genomes and built synthetic bacterial communities of varying composition and complexity in the laboratory, a method called reconstitution. They inoculated these communities onto three different host plants grown in soil: Arabidopsis thaliana, a small flowering plant widely used as a model organism in plant research, barley, a major cereal crop, and Lotus japonicus, a model legume. The researchers then sequenced which bacteria actually established themselves on each plant’s roots, but instead of stopping at which species won out, they also mapped what metabolic and signaling functions those species carried.

A Blueprint for Designing Biostimulants

The result was that, although each of the three plants ended up hosting a different mix of bacterial species, the functional output converged. Across all three plant hosts, the team identified 266 bacterial functions, about 3 percent of the total functional diversity present in the starting pool of genomes, that were consistently enriched in the root microbiome in every case. No single bacterial strain carried this entire set of functions; instead, the functions were distributed across multiple members of each community, forming what the researchers describe as a core functional toolkit for successful root colonization.

The three plant species also differed in how they assembled that toolkit. Arabidopsis and barley ended up with root communities shaped mainly by whatever bacteria happened to be most available in the surrounding inoculum, while Lotus japonicus favored a smaller number of generalist bacterial strains that each carried a broad mix of the needed functions on their own, an approach the researchers likened to a “Swiss army knife” strategy.

For companies that develop microbial biofertilizers and biostimulants, the practical implication is a different way of designing products. Much of today’s biologicals development proceeds by testing individual bacterial species or fixed strain combinations and seeing what works through trial and error on different crops and in different soils, a slow and often inconsistent process. The Aarhus and Utrecht team’s findings suggest that developers could instead screen candidate microbial consortia for the functional capacities they bring to a root system, rather than for a fixed list of species, since it appears to be the function a bacterium performs, not its taxonomic identity, that the plant is actually selecting for. That could make it easier to build microbial products that are more consistent across different crops and soil conditions, rather than products validated in one setting that underperform when moved to another.

Why It Matters for the Biologicals Industry

Biologicals, including microbial biofertilizers, biostimulants and biopesticides, are one of the fastest growing segments of the global agri-input industry, and India has been actively expanding registration pathways and promoting microbial consortia products as part of a broader push to reduce dependence on synthetic fertilizer and pesticide. A function-based framework for designing microbial products, if adopted by input companies and research institutes, could help both multinational and domestic biologicals developers build products that are more reliably adapted to local soils and climates, addressing a frequent complaint that microbial products developed and validated largely in temperate research settings underperform once moved to the tropical or semi-arid soils common across much of India and other developing agricultural markets.

The findings so far come from controlled laboratory reconstitution experiments rather than open field trials, and the authors have not yet published data on whether function-based consortia designed using this framework outperform conventional strain-based products under real farming conditions. That translation from laboratory principle to field-tested product is the next step the broader biologicals industry will be watching for.

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