Scientists resurrect 700-year-old viruses, Just in time for Halloween!
You know how some zombie movies start with a discovery of a virus, it gets loose, and things quickly spiral out of control from that? Well in breaking news a team of researchers have found two 700-year-old viral sequences in frozen caribou dung in an arctic ice patch. The group isolated part of a viral RNA genome and the complete genome of a DNA virus. Then they infected living plants with the DNA virus, what could go wrong?
So the big question is why would anyone do something so seemingly crazy, well scientists don’t know much about how viruses evolve. Understanding the structure of ancient viruses would increase knowledge of virus evolution. However, scientists have sequenced only a small number of ancient viruses.
The problem scientists run into is that reconstructing ancient viruses is difficult because they change very rapidly. This makes it hard to see how new sequences are related to one another. If that wasn’t problem enough, the nucleic acid content of ancient viruses can degrade quickly.
In a quest to find well preserved ancient viruses, the team analyzed layers of caribou feces in a 4,000-year-old ice patch in Canada’s Selwyn Mountains. When examining nucleic acids in frozen fecal pellets extracted from a 700-year-old ice layer, they identified two sets of well preserved viral sequences.
One of these was part of the genome of an RNA virus, which the researchers identified as belonging to the insect-infecting genus Cripavirus. So how did it get there, well they think caribou may have ingested insects infected with the virus. Insects attracted to the caribou or the feces may also have deposited the virus on the feces and the surrounding snow.
The team was able to reconstruct the entire genome of a DNA virus from the other viral sequence. This virus did not closely resemble any modern sequenced virus. However, the team discovered distant relationships with a group of plant-infecting viruses called geminiviruses and with gemycircularviruses (yea a mouthful I know), found in dragonflies, fungi and animal feces.
To learn more about the DNA virus, the researchers introduced it to the plant Nicotiana benthamiana, which scientists often use as a model when studying the infectivity of cloned geminiviruses. The virus replicated itself in inoculated as well as newly emerging leaves, evidence of infection. However, the infected plants did not develop any disease symptoms. The researchers suggest this could be because Nicotiana benthamiana is not the ideal host for this virus.
The group believes that caribou ingested the DNA virus when eating plants. Earlier studies have shown that viruses can remain infectious after passing through the digestive tracts of animals that have eaten virus-infected plants, insects or animals.
The researchers believe that as climate change speeds up the melting of arctic ice, more viral particles, which might remain infectious, could escape into the environment. The interesting issue with that is the big unknown factor. Sure this virus was something that infected plants, but there is nothing to say a virus could be found which would do the same to people.
Of course the introduction might have been a little over the top, but in Halloween spirit, I figured I would go a little crazy. The real point of this research however, is to insure that we know how virus’ change over time. This helps predict what might come next; in the process it will hopefully help us better improve vaccines, find new vaccines, and prevent deadly outbreaks we might have otherwise never seen coming.
You know like a real life horror movie or something.
Ng, T., Chen, L., Zhou, Y., Shapiro, B., Stiller, M., Heintzman, P., Varsani, A., Kondov, N., Wong, W., Deng, X., Andrews, T., Moorman, B., Meulendyk, T., MacKay, G., Gilbertson, R., & Delwart, E. (2014). Preservation of viral genomes in 700-y-old caribou feces from a subarctic ice patch Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1410429111