When Dr. Eman M. Othman-Sholkamy and her team at the University of Würzburg began analyzing blood samples from mice, they weren’t looking for plant hormones—they found them anyway. Cytokinins, long believed to be the exclusive domain of plants, where they regulate growth and stress responses, have now been detected in the bloodstream and organs of five mammalian species, including humans. This unexpected discovery, published in Gut Microbes, is rewriting textbook assumptions about the boundaries between plant and animal biology.
For decades, cytokinins were seen as botanical signals with no role in mammals. But the Würzburg team, led by Othman-Sholkamy and bioinformatician Thomas Dandekar, has shown these molecules are not only present but systematically distributed through vital organs like the heart, liver, and kidneys. What’s more, they’re not just passive hitchhikers—they appear to be functional, with potential roles in muscle development, nerve protection, and the regulation of cellular aging. The concentrations in human blood serum are four to ten times lower than in plants, but that doesn’t make them irrelevant. In biology, even trace signals can carry profound meaning.
The researchers traced cytokinins to three main sources: diet, gut bacteria, and the body’s own genes. Fasting mice showed a sharp drop in cytokinin levels within eight hours, pointing to food as a primary supply. Germ-free mice, lacking a natural microbiome, had significantly lower levels, while metagenomic analysis of 2.3 billion gene sequences from the Global Microbial Gene Catalog revealed specific bacterial strains capable of producing these hormones. Even more surprising, the human TRIT1 gene—present in our own DNA—may enable limited endogenous production. The team also identified cytokinin O-glucoside, an inactive storage form that can be activated when needed, suggesting a sophisticated regulatory system at play.
This isn’t just about where cytokinins come from—it’s about what they might do. Their presence in peripheral tissues raises the possibility they influence fundamental processes like immune response and long-term cellular health. As Othman-Sholkamy notes, these hormones could be quiet orchestrators of physiological balance, shaped by both what we eat and the trillions of microbes in our gut.
The implications for medicine are tantalizing. If cytokinins help protect nerve cells or modulate inflammation, they could open new pathways for treating neurodegenerative diseases like Huntington’s or chronic inflammatory conditions. With 20 studies already under their belt on cross-kingdom signaling and redox stress protection, this team is poised to lead a new frontier in microbiome and hormone research. As science begins to blur the lines between plant and animal, one thing is clear: the body’s chemistry is more interconnected—and more surprising—than we ever imagined.