by Alissa Zhang
Are you a fan of post-apocalyptic movies? Have you watched The Day After Tomorrow? I Am Legend? Or Contagion? Sometimes, real life is almost as strange as fiction, as recently global warming has led to the discovery of a giant virus frozen for the past 30,000 years in the Siberian permafrost. While the virus is unlikely to cause a zombie apocalypse, it does have the potential to harm modern organisms, and demonstrates yet another detrimental consequence of global warming that few are aware of. However, it could also be a key element in understanding the history of viruses and their biological processes.
The discovery of Mollivirus sibericum was announced in September 2015 by a team of French scientists from the Laboratoire Génomique et Structurale, the Laboratoire Biologie à Grande Echelle, and the Genoscope.1 Astrobiologists from Russia have taken core samples buried deep in Siberian permafrost to look for signs of life, using these as models for explorations for potential life on Mars. The French team obtained some of these samples, and under isolated conditions mixed parts of the permafrost samples with the amoeba Acanthamoeba, hoping to draw out any dormant viruses. If the amoeba died, the French scientists could know that a virus must have been present in the sample; they could then isolate it to study it.2 This discovery marks the first time that genomics, transcriptomics, proteomics, and metagenomics—all classes of analytical techniques applicable to living organisms—were simultaneously used to characterize a virus.3
The name of the virus comes from molli, a French word that roughly translates to soft or flexible, and sibericum, for the location where it was found. The virus is a roughly spherical particle, approximately 0.6 μm long, and contains a genome of approximately 650,000 base pairs coding for over 500 proteins.3 While its size barely qualifies it as a giant virus, the size of its genome is enormous compared to many modern viruses. For example, HIV has only nine genes, and Influenza A only eight. Mollivirus uses the cell nucleus to replicate in the amoeba, which makes it host-dependent like most viruses. Its method of replication and other characteristic traits, such as a deficiency in certain key enzymes that allow synthesis of its DNA building blocks, make Mollivirus similar to common modern viral types, including human pathogens like Adenovirus (which causes respiratory infection), Papillomavirus (which includes HPV), or Herpesvirus (which includes herpes, mononucleosis, and chickenpox).3
Mollivirus is not the first giant virus to be revived from the Siberian permafrost. Three other giant viruses have previously been discovered in the same samples — Megaviridae (2003), Pandoraviridae (2013), and Pithovirus (2014)—using similar techniques. However, Mollivirus differs from these families of viruses in its shape, mode of replication, and metabolism. For example, the proteins of Mollivirus and Pithovirus bear little resemblance to each other. In addition, Pithovirus only requires host cytoplasm to multiply. This makes Pithovirus more similar to Poxvirus, a family that includes the now-eradicated smallpox virus.4 The discovery of Mollivirus suggests that ancient giant viruses are not rare, and are highly diverse. It also proves that a variety of virus families, with different and potentially pathogenic characteristics, can survive in permafrost for thousands of years.
Although the analysis of the Mollivirus sample revealed very low concentrations of the virus, this discovery has important implications for public health. Only a few infectious viral particles are needed to cause the resurgence of an ancient virus. The rapid pace of global warming in recent years exacerbates this risk, as Arctic temperatures are rising at more than twice the global average, and permafrost is melting.5 Climate change has opened up new sea routes through Arctic ice, facilitating accessibility and industrial exploitation of Arctic regions that hold valuable mining and oil resources. An increasing number of companies are already mining for gold and tungsten in northern Siberia, which will lead to the excavation of millions of tons of permafrost that have been buried for thousands of years, much like the core sample that revealed these four giant viruses.2 There is no way of predicting what that volume of permafrost may contain. Without safeguards in place, there is real risk of reviving potentially pathogenic viruses thought to be long extinct. Even modern viruses may be preserved in upper layers of permafrost.5
On the other hand, these giant viruses also hold promise for advancing scientific knowledge. Scientists may be able to find new metabolic pathways and biochemical processes that can be used to produce new pharmaceuticals and biomolecules. These ancient viruses may provide insights into the history of viral evolution, or even the origin of life.2
To better understand both the risks and rewards posed by unearthing Mollivirus and other giant viruses, the French team is now digging even deeper into the Siberian permafrost, with the goal to aptly study samples from a million years ago.
Alissa Zhang ‘16 is a senior in Currier House, concentrating in Chemical and Physical Biology.
- Legendre, M. et al. PNAS 2015, 112, E5327-E5335.
- Christensen, J. Ancient squirrel’s nest leads to discovery of giant virus. CNN [online]. September 11, 2015. http://www.cnn.com/2015/09/11/health/ancient-squirrel-leads-to-giant-virus-discovery/ (accessed October 4, 2015).
- CNRS. New giant virus discovered in Siberia’s permafrost. Centre National de la Recherche Scientifique [online], September 7, 2015. http://www2.cnrs.fr/en/2617.htm (accessed October 4, 2015).
- Legendre, M. et al. PNAS 2014, 111, 4274-4279.
- Frankenvirus emerges from Siberia’s frozen wasteland. Phys.org [online], September 8, 2015. http://phys.org/news/2015-09-frankenvirus-emerges-siberia-frozen-wasteland.html (accessed October 4, 2015).