Gut microbes are essential partners that help digest food, produce vitamins and train the immune system. They can also pass on behavioral traits to their host’s offspring, at least in mice. Scientists at the Max Planck Institute for Biology Tübingen have discovered that the mouse microbiome can alter the animal’s behavior in just four generations, independent of its genes. The study is published in the journal Nature Communications.
Animals and their microbes have coevolved for millions of years. While it was already known that bacteria, viruses and fungi living in the gut can drive inherited changes in some simple creatures, like insects, scientists didn’t know whether they could be the sole mechanism for passing down a specific trait (like a behavioral tendency) in more complex animals, such as mammals.
The experiment
The research team designed an experiment in which they strictly controlled the host animal’s genes. First, they took gut microbiota from wild-derived mice and gave it to genetically identical germ-free mice in the lab.
Then they set up a selection line, repeatedly choosing the two mice that traveled the least and transferring their microbes into a fresh batch of genetically identical, germ-free mice for the next generation. The scientists focused on locomotor activity (movement) because previous tests had confirmed that it was a behavior strongly influenced by the microbiome. The researchers also ran a control line where two donor mice were chosen at random.
This serial transfer of gut microbes carried on for four generations. By using germ-free mice, the researchers could be sure that any behavioral changes they observed were due to the selection and transfer of the microbial community.
Microbes passing down traits
Selecting for low activity successfully caused slower movement across the four generations. The researchers analyzed the composition of the microbial community and found that this reduction in activity was linked to higher levels of the bacterium Lactobacillus, which produces the substance indolelactic acid (ILA). They also showed the link was causal. When they independently gave Lactobacillus or ILA to other mice, it was enough to suppress their locomotion.
“Our work highlights the role of microbiome-mediated trait inheritance in shaping host ecology and evolution,” wrote the researchers in a paper.
“The novelty in our study lies in experimentally demonstrating that selection on a host trait can lead to changes in that same trait over time purely through microbiome transmission, without any genetic evolution in the host.”
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More information:
Taichi A. Suzuki et al, Selection and transmission of the gut microbiome alone can shift mammalian behavior, Nature Communications (2025). DOI: 10.1038/s41467-025-65368-w
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