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Siberian Permafrost Reveals Ancient Giant Virus, Remains Infectious

March 4, 2014
Image Caption: Transmission electron microscopy color image of a Pithovirus sibericum cross-section. This virion, dating back more than 30,000 years, is 1.5 μm long and 0.5 μm wide, which makes it the largest virus ever discovered. Credit: Julia Bartoli & Chantal Abergel, IGS, CNRS/AMU

Lawrence LeBlond for redOrbit.com – Your Universe Online

Giant viruses may seem like the latest creation in a Hollywood B movie production, but the recent discovery of a larger-than-life virus buried in ice is definitely no science-fiction tale. A husband-and-wife team from Aix-Marseille University in France have discovered a monster virus that has been buried in Siberia’s permafrost for the past 30,000 years.

Jean-Michel Claverie and Chantal Abergel, who led the discovery, have named this new creature Pithovirus sibericum, inspired by the Greek word ‘pithos’ for the large container used by ancient Greeks for food and wine. “We’re French, so we had to put wine in the story,” joked Claverie.

While the discovery is significant for science, it is more so for health, as the virus has been found to still be infectious. However, this predator only preys on amoebae.

Still, the researchers warn that as Earth’s ice caps and glaciers melt around the world, more and more viruses, perhaps buried for thousands or millions of years, could reemerge and potentially become global human health risks.

The newly discovered P. sibericum is not only a giant virus – it is the largest one ever found. At 1.5 micrometers long, it is about 50 percent larger than the previous record holder (Pandoraviruses), which were also discovered by Claverie and Abergel. The husband-and-wife team discovered their first giant virus in 2003, named Mimivirus.

While these viruses are by no means giant in the normal sense of the word, which may conjure up images of mammoths, dinosaurs and whales, they are loosely defined as giants because of the fact that they can be seen using a standard microscope, according to the team.

“Once again, this group has opened our eyes to the enormous diversity that exists in giant viruses,” Curtis Suttle, a virologist at the University of British Columbia in Vancouver, Canada, who was not involved in the work, told Nature’s Ed Yong.

Claveria and Abergel’s latest work, published in the journal Proceedings of the National Academy of Sciences, is based partly on a study from a few years earlier.

After learning that Russian scientists had resurrected an ancient plant from fruits entombed in Siberia’s permafrost for the past 30,000 years, they wondered if would be “possible to revive a virus.”

Using the permafrost samples provided by the Russian team, Claverie, Abergel and their colleagues fished for giant viruses using amoebae as bait. The team discovered the giant virus particles inside these amoebae as they started dying.

COMPLEX CREATURES

Surprisingly, these newly discovered pathogens are not only large in size, but very complex as well. P. sibericum has been found to contain 500 genes. Despite being larger than the previously discovered Pandoravirus, it pales in comparison to that pathogen’s 2,500 genes.

Still, these viruses are off the chart when compared to other more common viruses. James Van Etten, a professor of plant pathology at the University of Nebraska, explained to NatGeo’s Stefan Sirucek that the HIV virus has only about 12 genes.

The researchers noted that giant viruses are not only bigger, they are also much hardier than others. They surmise that this hardiness, along with a favorable environment, helped P. sibericum remain intact in its ice entombment. More often than not, viruses are either destroyed or rendered inactive by several factors – light and biochemical degradation are two main factors.

“Among known viruses, the giant viruses tend to be very tough, almost impossible to break open,” said Claverie and Abergel in the Nature article. “Special environments such as deep ocean sediments and permafrost are very good preservers of microbes [and viruses] because they are cold, anoxic [lacking oxygen], and in the dark.”

The study of this new pathogen has revealed some pretty surprising properties.

Looking at the virus under a microscope, P. sibericum appears as a thick-walled oval with an opening at one end, very similar to Pandoraviruses. But despite their similar shapes, Pithoviruses are “totally different viruses,” said Abergel.

Pithovirus has a ‘cork’ with a honeycomb structure capping the opening. Contrary to other viruses, which copies themselves by taking over the nucleus, this giant builds replication factories in its host’s cytoplasm. The team noted it was surprising to find that the Pithovirus genome is so much smaller than that of the Pandoravirus, despite its larger size.

“That huge particle is basically empty,” says Claverie. “We thought it was a property of viruses that they pack DNA extremely tightly into the smallest particle possible, but this guy is 150 times less compacted than any bacteriophage [viruses that infect bacteria]. We don’t understand anything anymore!”

IMPACT ON HUMAN HEALTH

Although giant viruses are known to mainly attack amoebae, at least one giant virus was discovered that could pose a threat to human health.

Christelle Desnues, a virologist at the French National Centre for Scientific Research in Marseille, discovered in 2013 that the giant Marseillevirus had infected an 11-month-old boy.

The boy had been hospitalized with inflamed lymph nodes and upon a blood analysis, Desnues and her team discovered traces of the virus’ DNA. They then found the virus itself in the lymph nodes.

“It is clear that giant viruses cannot be seen as stand-alone freaks of nature,” she told Yong. “They constitute an integral part of the virosphere with implications in diversity, evolution and even human health.”

Discoveries like these are alarming, and scientists, Claverie and Abergel included, are concerned about the continuing rise in temperatures, as well as the mining and drilling operations in the Arctic. Together, these factors offer the chance for more ancient infectious viruses to emerge and become threats to human health around the world.

However, Suttle said that the likelihood of a killer virus emerging from the Arctic ice is very remote. People already are bombarded by millions of viruses on a daily basis and to think that the melting ice would release harmful viruses that could circulate enough to impact human health, “stretches scientific rationality to the breaking point,” he noted.

“I would be much more concerned about the hundreds of millions of people who will be displaced by rising sea levels,” he told Nature’s Yong.

Claverie and Abergel have maintained that they are not attempting to “revive” Pithovirus, or any other giant virus for that matter, but rather hoping to determine the potential danger from such pathogens.

“If we find some [human pathogens], then the risk will become more real. If not, we will be safe,” they concluded.


Source: Lawrence LeBlond for redOrbit.com - Your Universe Online



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