Lab-grown microbes show drastically different behavior on living plants

A corn root bacterium in a petri dish and the same bacterium on a living plant are, functionally speaking, two different organisms. Researchers at North Carolina State University grew seven species of corn root bacteria in both settings and discovered that every single one underwent a radical transformation the moment it encountered its host plant. The shift was not subtle—thousands of genes flipped on or off, rewriting the microbe's entire operational manual.

Anna Garrell, the postdoctoral researcher who led the work, described the finding as a corrective to decades of microbiology practice. In the lab, scientists have relied on controlled environments to understand how microbes behave, and those experiments remain valuable. But they tell an incomplete story. "What you find in the lab is not necessarily what's going to be happening in the real environment," Garrell said. The study, published in mSystems in August 2026, measured the protein expression of seven bacteria species both in vitro and in planta—on the actual plant—to quantify exactly how much their behavior diverged.

The specifics of that divergence varied dramatically by species. Some bacteria, upon reaching the root, became more motile and activated genes that would help them move and swim through the soil. Others did the opposite: they settled onto the root surface, became stationary, and began secreting compounds to attach themselves firmly to the plant. A few activated systems to solubilize phosphate, making nutrients more available. Others shifted their metabolism to consume different sugars. The diversity of response was itself striking. "All these bacteria interacted with the plant very differently," Garrell observed. "Not all bacteria are made the same, nor do they interact with the plant the same."

Manuel Kleiner, the principal investigator and an associate professor of plant and microbial biology at NC State, emphasized the sheer magnitude of the reprogramming. "It's not just ten or so genes, it's thousands that completely shift as soon as they start interacting with the plant," he said. The microbes were not making minor adjustments to their behavior. They were fundamentally rewriting their programming in response to the presence of a living host.

The researchers chose their test subjects carefully. The seven bacteria came from what scientists call a defined community—a stable group of microbes with known genomes and known origins. All seven colonize corn roots consistently and reliably, making them ideal for controlled comparison between lab and plant environments. This stability allowed the researchers to isolate the variable: the presence or absence of the living plant.

The implications reach beyond basic science. Understanding how microbes actually behave on plants—not how they behave in isolation—could reshape the development of agricultural products. If scientists want to engineer microbial communities that improve crop health or reduce the need for chemical inputs, they need to know what those microbes will actually do when they encounter a living root. The current study opens the door to more sophisticated questions: How do multiple microbes influence each other when they're all on the same plant? How do they coordinate to colonize roots more effectively? What chemical signals pass between plant and microbe to trigger these behavioral shifts?

Garrell framed the work as a foundation for the next phase of research. "This will be important for developing real products to use in sustainable agriculture," she said. The study was funded by the USDA National Institute of Food and Agriculture, the Novo Nordisk Foundation, and the National Science Foundation, reflecting the recognition that understanding plant-microbe interactions at a molecular level has practical consequences for food production and environmental stewardship.