Revived giant virus from the eternal ice

Researchers bring 30,000 years old giant virus to life

04/03/2014

Awakening giant viruses from the Arctic? Climate change may carry unprecedented risks. A team of French and Russian scientists has thawed viruses from the 30-meter deep permafrost of northeastern Siberia and brought them back to life. The 30,000-year-old viruses are significantly larger than all previously known giant viruses, the researchers report around Matthieu Legendre and Julia Bartoli from the University of Aix-Marseille in the journal „Proceedings of the National Academy of Sciences“ (PNAS).

So far, according to the researchers, two very different species of giant viruses were known. The viruses of the genus Megaviridae, as the prototype of which was identified ten years ago Mimivirus, and the viruses from the recently discovered genus of Pandoraviruses. Now the researchers have identified in the permafrost a further genus of giant viruses, the properties of both previously known genera combined - the pithovirus sibericum. After 30,000 years in eternal ice, the viruses were revived and were immediately active again. The researchers evaluated this „as a safe indicator of the possible presence of pathogenic DNA viruses in permafrost.“ As global warming or industrial exploitation (especially oil drilling) deepens, soil may not be able to rule out future threats to human health from revived viruses, concludes Legendre and Bartoli.

Viruses of exceptional size and survivability
When a core of Siberian permafrost was thawed, the previously unknown giant viruses awoke, which subsequently led to a fatal infection on contact with a potential host - amoebae of the genus Acanthamoeba - the scientists write. The viruses were revived after 30,000 years at average temperatures of minus 18 degrees Celsius. Exceptional was not only this unique survivability of the viruses, but also their enormous size. The viruses were visible in the following studies under the light microscope. They reached a size of 1.5 microns in length, but had a surprisingly small genome compared to other giant viruses, report Legendre and Bartoli. In its size the pithovirus sibericum surmount many bacteria and unicellular parasites.

Newly discovered viruses combine the property of other giant viruses
Viruses over one micron in size were considered unthinkable for a long time before the first giant viruses were discovered more than ten years ago. Meanwhile, the number of reports of newly identified species of giant viruses. They are found in different places. For example, in the summer of last year, the report about giant viruses in sea mud off the coast of Chile went around the world. The previously detected viruses could be assigned to two different genera: the Megaviridae and the Pandoraviruses. According to the researchers, the newly discovered pathogens combine the properties of both genera. For example, the amphorus-like form corresponds to the pandoraviruses, but the genome is more reminiscent of the viruses of the genus Megaviridae.

Giant viruses a growing threat in the context of climate change?
The scientists conclude that the family of giant viruses may be significantly larger than previously thought. Whether there are also viruses that can be dangerous for humans, remains open so far. „The revival of such an ancestor of the amoeba-infecting viruses can be considered as a reliable indicator of the possible presence of pathogenic DNA viruses in the permafrost“, reports the Russian-French research team. At worst, climate change brings with it a massive spread of hitherto unknown viruses, which means that future threats to human health can not be ruled out. (Fp)

Picture: Aka