The team recreated the code of a complete DNA and one partial RNA viral genome from 700-year-old caribou feces.
Viruses preserved in ancient samples provide valuable information about viral diversity from long ago; they help us trace how today's species evolved and study their biology.
However, it is not easy to recreate ancient viruses. Even when they are preserved in ancient specimens, they are somewhat degraded and their concentrations are low.
Now, a new study led by the University of California, San Francisco (UCSF), shows how it is possible, using modern techniques in the field of molecular genetics, to recreate ancient viruses from cryogenically preserved materials.
Senior author Eric Delwart, an Adjunct Professor in UCSF's Department of Laboratory Medicine, and colleagues report their findings in the Proceedings of the National Academy of Sciences.
The team resurrected two ancient viruses and showed one could infect a plant
The method the team used to resurrect the ancient viruses is called "viral particle-associated nucleic acid enrichment."
In their paper, they describe how using this approach they recreated the code of a complete DNA and one partial RNA viral genome from 700-year-old caribou feces recovered from a subarctic ice patch in the Selwyn mountains of the Yukon and Northern Territories, in Canada.
The authors write:
"We were able to recover and characterize two viruses in replicated experiments performed in two different laboratories: a small circular DNA viral genome (ancient caribou feces associated virus, or aCFV) and a partial RNA viral genome (Ancient Northwest Territories cripavirus, or aNCV)."
Then using "reverse genetics," they reconstituted one of the viruses and showed it was able to spread and reproduce in a living plant.
The team says their findings show that under frozen conditions, "encapsidated viral nucleic acids" can survive for centuries, providing enough material to allow "molecular genetics to regenerate viruses to study their biology."
Will global warming resurrect old, infectious viruses?
The study findings raise the question of whether dormant, potentially infectious pathogens will emerge if global warming melts enough ice and permafrost. What might the consequences be for people and wildlife?
Prof. Delwart says there is a theoretical risk of this: "the nucleic acid of the virus was in great shape in our sample," he notes in a report on the study by New Scientist.
"But old viruses could only re-emerge if they have significant advantages over the countless perfect viruses we have at present," he adds.