New York: A 30,000-year-old giant virus discovered deep in the Siberian permafrost is still functional and capable of infecting its host, researchers have found.
However, the new virus is not a threat to humans; it infected single-celled amoebas during the Upper Paleolithic, or late Stone Age.
Dubbed Mollivirus sibericum, the virus was found in a soil sample from about 98 feet below the surface.
M sibericum is a member of a new viral family, the fourth such family ever found.
Until about a decade ago, viruses were thought of as universally tiny and they were isolated by filtration techniques that strained out larger particles, said Chantal Abergel, a scientist at the National Center for Scientific Research at Aix-Marseille University in France.
But after the discovery of an amoeba-infecting giant virus called Mimivirus, first reported in the journal Science in 2003, researchers widened their search for bigger viruses.
Since the discovery of the Mimivirus family, researchers have discovered the Pandoraviridae and Pithoviridae families - the latter discovered in the same soil sample as M sibericum and reported by Abergel and her colleague Jean-Michel Claverie in 2014.
M sibericum is wider in diameter than the other giant viruses discovered, at 600 nanometres versus 500. It has a genome of 600,000 base pairs which hold the genetic instructions to create 500 proteins.
Viruses are snippets of RNA or DNA that work by hijacking a cell's machinery to carry out these instructions.
"We are now at the stage where there are four families of giant viruses, and we can say that they are much more diverse [than previously known]," Abergel told 'LiveScience'.
The researchers' technique to isolate and study these viruses does not pose a threat to humans or animals, Abergel said, but it's possible that dangerous viruses do lurk in suspended animation deep belowground.
These viruses are buried deep, so it's likely that only human activities - such as mining and drilling for minerals, oil and natural gas - would disturb them.
The discoveries of the giant viruses signal that they can remain infectious for at least tens of thousands of years, Abergel said. So far, however, scientists have yet to discover any ancient human-infecting giant viruses.
The research appeared in the journal Proceedings of the National Academy of Sciences.