For 40 years, scientists blamed the wrong suspect — this gut virus infects bacteria, not people

Picobirnavirus has been turning up in human stool samples for nearly four decades, and scientists assumed it infected people and caused stomach illness. A team led by Washington University School of Medicine in St. Louis has now shown that is not true: the virus infects gut bacteria instead. Using microbe-free mice and lab dishes of gut bacteria grown without oxygen — conditions human cells cannot survive — they watched the virus multiply only when bacteria were present, and antibiotics that killed the bacteria stopped it cold. Published in Nature Microbiology, the finding makes picobirnaviruses only the third known family of RNA viruses that infect bacteria, and it changes how researchers will study the trillions of microbes, and their viruses, living in our guts.