Drunken graduate student discussions about the role of viruses in human development have taken on new importance now that researchers studying mice have shown that a virus can help maintain and restore a healthy gut in much the same way that friendly bacteria do.

The work “shows for the first time that a virus can functionally substitute for a bacterium and provide beneficial effects,” says Julie Pfeiffer, a virologist at the University of Texas Southwestern Medical Center in Dallas who was not involved with the study. “It’s shocking.”

Our bodies are mostly microbes, with each of us hosting a hundred trillion bacteria as our so-called microbiome. These bacteria appear to play a role in everything from our weight to our allergies. But viruses also lurk in and around those bacteria—and they vastly outnumber the microbes.

Like the microbiome, this “virome” may be important for human health. One recent study, for example, found that viruses that are abundant in saliva may weed out harmful bacteria. Kenneth Cadwell, a virologist at New York University School of Medicine in New York City, wanted to know what viruses in the gut might be doing. In particular, he was interested in a group called noroviruses. Although they are notorious for causing epidemics of diarrhea on cruise ships and disease in lab mouse colonies, some noroviruses infect mice with no ill effects.

Reminds of this scene from 1978’s Animal house, but I could only find the clip in this other language.