Joint Russian-French team found a new giant 30 000-year-old virus which parasitizes on amoebas in Siberian permafrost.
The new virus called Mollivirus sibericum is described in a paper in Proceedings of the National Academy of Sciences. The authors are Yelizaveta Rivkina (Institute of Physicochemical and Biological Problems of Soil Science - ISSP), French colleagues under the guidance of Jean-Michel Claverie (Mediterranean Institute of Microbiology), and Lyubov Shmakova (a KFU alumnus, now Senior Research Associate of the Soil Cryology Lab at ISSP).
She is currently studying Amoebozoa found in permafrost.
Dr. Shmakova told Kazan University newspaper about this new discovery and previous record holders - Mimivirus and Pandoravirus.
During the years of work of the Soil Cryology Lab in the Arctic and the Antarctica many new organisms have been found which are now stored in the lab's collection.
- A yearly expedition called "Beringia" works in the Russian Arctic, on the shores of the Kara Sea, the Laptev Sea, and the East Siberian Sea. The main goal of those trips is collecting frozen samples. This new giant Mollivirus sibericum was found in a frozen soil sample collected near Kolyma in 2000. The viruses are called giant if they are more than 1 micron in size.
A joint project with French colleagues began in 2012 with a PNAS publication about Silene stenophylla which was reproduced from a 30 000-year-old seed. Researchers from the Mediterranean Institute of Microbiology suggested exploring permafrost samples for giant viruses.
- The collaboration was structured as follows - ISSP in Russia sampled and categorized permafrost, determined its age, and our peers in Marseille found and studied strains of amoebas.
Dr. Shmakova reminded that the history of giant viruses started with Mimivirus in 2003.
- It was called so because of its ability to imitate bacteria. By the way, when it was first discovered in 2001, the scientists didn't even recognize it as a virus. Later some other giant viruses were discovered, such as Marseillevirus, Mamavirus; they parasitize not only on Acanthamoeba but on other Protozoa as well.
The second family of giant viruses - Pandoraviridae - was discovered in 2013. And a species Pithorivus sibericum of the third family was described in 2014.
- It turned out that amoebas from a 30 000-year-old Siberian permafrost are resistant to contemporary megaviruses. Pithovirus sibericum now holds the record for the largest known virus - it's 1.5 microns in length.
And now Mollivirus sibericum - a representative of the fourth megavirus family - is presented to the public.
All the newest life science research methods - genomics, transcriptomics, proteomics, metagenomics - were used to study and classify the virus.
- It resembles the previously discovered Pandoravirus - oval-shaped, with thin walls and oblong envelope; it's 0.6 microns long, and its genome has 650 thousand base pairs coding more than 500 proteins. The majority of these proteins have nothing in common with Pithovirus sibericum. Moreover, unlike Pithovirus, Mollivirus uses not only cytoplasma but also an amoeba's nucleus which makes it dependent on the host like the majority of "smalll" viruses.
The researchers united their efforts and started some sort of a "fishing" experiment - they tried to lure viruses in permafrost using amoebas as bait. And a virus was indeed found in a dead amoeba afterwards.
Dr. Shmakova added that these new viruses are not only much larger than their relatives but also more genetically complex. Mollivirus has more than 500 genes, Pandoravirus - more than 2 500. For comparison, genomes of influenza viruses contains 6 - 7 individual RNA molecules.
The findings are more evidence of the real diversity of the world of viruses which is now only starting to open its secrets to the science.
- New tech allows us to see how parasites become symbionts, and symbionts become organelles, how they exchange genetic information and fight each other. Four new families of viruses were discovered in such a short timespan. This shows that microorganisms - viruses included - can survive in permafrost for the longest periods of time.
What about danger to humans? Evidently, Mollivirus is not in any way dangerous to humankind or animals.
- Seems like amoebas and this virus have a longstanding "relationship" which led to this kind of gigantism and different life cycles of the viruses. This particular giant virus from Kolyma permafrost is no danger to a human being whatsoever, it only parasitizes on amoebas.
However, the ongoing climate change in the Arctic, industrial activities in the region can lead to the revival of some other pathogenic organisms. Melting Arctic ice can produce ancient microorganisms which have been stored there for thousands and millions of years. And it's very difficult to predict what they can bring.