Scientists Trace a Common Gut Virus to Bacteria, Not Human Cells

A virus long associated with the human digestive tract infects gut bacteria rather than human cells, researchers at Washington University School of Medicine in St. Louis and their collaborators reported Thursday. The finding offers a new way to investigate a group of viruses that has puzzled scientists for decades.

The study, published in Nature Microbiology, examined a human gut-associated picobirnavirus. These viruses were first identified in stool samples from people with diarrhea and have since been linked with several health conditions. Those associations had not established whether the viruses caused disease or which cells they infected.

Researchers introduced human stool samples into microbe-free mice, creating a laboratory model in which the virus could multiply. They then grew the virus with gut bacteria under oxygen-free conditions. Its continued growth, and the fact that antibiotics halted that growth by killing the bacteria, helped point to a bacterial host.

Using molecular imaging and cell sorting, the team identified the virus inside a newly identified bacterium called Candidatus Anaerotignum faecalis. The work establishes picobirnaviruses as the third known major group of RNA viruses that infect bacteria, according to the researchers.

The finding does not show that picobirnaviruses are harmless, nor does it prove they cause diarrhea, diabetes or other illnesses. They could affect health indirectly by changing bacterial communities or triggering inflammation. High levels of the virus might also be a marker of a disturbed gut ecosystem rather than its cause.

The immediate result is a research tool and a clearer biological target, not a new treatment. The WashU Medicine announcement describes how the finding could guide further studies of the microbiome and the viruses that live within it.