Scientific breakthroughs: “discovery of giant virus”

The discovery of a new giant virus, very different from the others, could revolutionize the definition of life and highlight one of the new scourges that threaten humanity in the event of global warming.

After the global thermonuclear explosion, the major climatic catastrophes, the meteorite rushing against the Earth, the conquest of the Martians (or any other being that is different and inconceivable physiologically, giant spiders, etc.), here is a new version of the Earth’s Apocalypse: the invasion of today’s world by yesterday’s giant viruses.

This could make one think of the trailer of a disaster movie, but the hypothesis is now plausible. Researchers have managed to “wake up” a giant virus that is 30,000 years old. This is the discovery announced on September 8, 2015 by the publication of an article on Mollivirus sibericum (available here) following work carried out by a laboratory on the Luminy campus in Marseille.

Since global warming, Siberian permafrost is melting. This has led to some discoveries, such as baby mammoths that have been frozen for 50,000 years. It would also make it possible to bring out in nature microorganisms that have been frozen for tens of thousands of years, or even hundreds of thousands and even millions of years.

4 new species of giant viruses

This isn’t the first giant virus we’ve discovered. It’s the fourth. The first one, called Mimivirus (Megavirus family), was announced on March 28, 2003 [B. La Scola et al, “A giant virus in amoebae”, “Science”, vol.299, n°5615, p.2033] by the same team under the direction of Didier Raoult and Jean-Michel Claverie. The viral character had been detected from an organism recovered in 1992 from an industrial air-conditioning tower in Bradford, England, and originally thought to be a bacterium. Mimivirus for “Mimicking microbe virus” but also to recall “Mimi the amoeba” whose father, a military doctor, imagined the adventures of Didier Raoult when he was a child to explain the theory of Evolution to him.

The same team led by Jean-Michel Claverie and Chantal Abergel, from the Laboratoire Information génomique et structurale de Marseille associated with the Laboratoire Biologie à Grande Échelle in Grenoble, the Génopole d’Évry, the Marseille hospitals, the CEA and INSERM, had discovered on 29 July 2013 one of two species of Pandoravirus (one in lake sediment in Melbourne, Australia and the other in coastal sediments in Chile) that total about one million base pairs and between 1,500 and 2,500 genes [N. Philippe et al, “Pandoraviruses: amoeba viruses with genomes up to 2.5 Mb reaching that of parasitic eukaryotes”, Science, vol. 341, n°6143, p.281].

This team had also succeeded in isolating Pithovirus sibericum from a 30,000-year-old ice core from Siberian permafrost. The giant virus then had novel properties [M. Legendre et al, ‘Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology’, PNAS, vol. 111, n°11, p.4274 published on 4 March 2014].

Mollivirus sibericum

It was also in the ice several hundred metres deep in the permafrost that researchers found the oxygen-deprived Mollivirus sibericum, which gave it a very high “instinct” for conservation.

Mollivirus sibericum is thus the fourth type of giant virus found in the world. Researchers have been able to replicate it by infecting amoebas of the genus Acanthamoeba. Fortunately, it is not dangerous for humans, but what is particularly surprising is that it is active again after 30,000 years of inactivity.

Before the scientific article was published, researchers ran it through a very fine toothpick of characterization, in particular to analyze its genome, its messenger RNAs (which transform genes into proteins), etc. The results of the study were presented in a paper published in the journal “The Science and Technology of the Acanthamoeba Genus”.

Its size is six tenths of a micrometre, which is not a record (held by the Pandoravirus; the Ebola virus can also reach one micrometre) but it is nevertheless very large, larger than some bacteria. Its genome is also very complex with 651,523 base pairs in its DNA. It should be remembered that the influenza or AIDS virus has only about ten base pairs, and the Ebola virus has only 19,000 base pairs despite its size.

Contrary to the previous giant viruses, the Mollivirus sibericum is very original. After multiplication, it recovers nearly a hundred proteins (this is a record), eleven of which are components of ribosomes, the protein factories located in the cytoplasm of host cells. Unlike ribosomes, viruses are not able to produce proteins with DNA information. This originality is still very mysterious because we don’t yet know what these proteins can be used for.