Scientists have discovered that viruses can latch onto other viruses to insert their genes into host cells. Lab results with apparent contamination led the team to directly see the strange interaction for the first time.

Viruses are known to infect the cells of host organisms like animals, plants, and even bacteria, but they’d never been known to physically attach themselves to other viruses before. The closest relationship is that between “helper” and “satellite” viruses, where the latter needs the help of the former to survive. Usually that means just staying close by, but in a new study scientists have spotted satellite viruses consistently latching onto their helpers.

The discovery started as part of a routine undergraduate project where bacteriophages – viruses that infect bacteria – are isolated from environmental samples and sent to labs for sequencing. In one sample, the DNA of an expected virus, called MindFlayer, was found, but the analysis reported contamination by unknown DNA. Repeated experiments returned the same results.

To find out what was happening, researchers then examined the samples using a transmission electron microscope (TEM). To their surprise, they discovered that the MindFlayer phage had a small satellite virus (dubbed MiniFlayer) attached to its “neck” section. And it wasn’t just a one-off occurrence either – 80% of the phages observed, or 40 out of 50, had an attached satellite phage. Even among those that didn’t have one at the time, some still bore “tendrils” that indicated they’d been bound by them in the past.

“When I saw it, I was like, ‘I can’t believe this’” said Tagide deCarvalho, first author of the study. “No one has ever seen a bacteriophage – or any other virus – attach to another virus.”

After the discovery, the team investigated what was going on by analyzing the genomes of the satellite and helper viruses, as well as the host. They found that unlike all other known satellite viruses, MiniFlayer was missing a gene that helped it integrate into the host’s DNA. This means it would need to stay near its helper, MindFlayer, in order to replicate inside a host cell.

“Attaching now made total sense, because otherwise, how are you going to guarantee that you are going to enter into the cell at the same time?” said Ivan Erill, senior author of the study.

Further work will be conducted to explore whether this is the correct explanation for the mechanism, and how common it might be among other viruses.

The research was published in the Journal of the International Society of Microbial Ecology.

Source: UMBC