Huge viruses may open 'Pandora's' box: French study

Jul 18, 2013 by Kerry Sheridan
The logo of the French National Centre for Scientific Research (CNRS) in Paris on December 7, 2012. Two newly discovered viruses are twice as large as the previous record-holders and may represent a completely new life form, French scientists reported in the US journal Science.

These viruses are so big they might just be your ancestors.

Two newly discovered viruses are twice as large as the previous record-holders and may represent a completely new life form, French scientists reported in the US journal Science.

Researchers say they were "extremely surprised" by the discovery of what they are calling "Pandoraviruses," which are not believed to be the type that make people sick.

Instead, what is most interesting about them is their giant-sized genome—from 1,900 to 2,500 genes—way more than viruses like , which has 10. Humans, by comparison, have about 24,000.

The previous record for a virus was 1,200 genes, in the discovery of the Megavirus chilensis. Before that was the Mimivirus with around 1,000 genes, discovered by the same team of scientists a decade ago.

Viruses are typically not deemed to qualify as a form of life, but some scientists say these merit consideration as a new kind of living object.

One, Pandoravirus salinus, was found on off the coast of Las Cruces, Chile.

The other, Pandoravirus dulcis, was found in the muck of a pond in Melbourne, Australia.

They are visible under a and look to have more in common with cells than other known viruses.

This picture shows the genome of Megavirus chilensisa, the previous record holder for largest virus, with 1,200 genes. Two newly discovered viruses are twice as big and may represent a completely new life form, French scientists reported in the US journal Science.

Pandoraviruses come from a different family than previously known giant viruses, said researchers Jean-Michel Claverie, a professor at the school of medicine at Aix-Marseille University and Chantal Abergel, director of research at France's National Center for Scientific Research (CNRS).

Their container-like shape and unique set of genes "made us associate them to the Pandora box. The opening of the box will definitively break the foundations of what we thought viruses were," the researchers said in an email to AFP.

Most of their genes appear unfamiliar to scientists, and they contain code for proteins and enzymes that "do unknown things," the authors said.

"The lack of similarity of most of their genes with other life forms might be an indication that they originated from a totally different primitive cellular lineage."

That means, according to the researchers, that Pandoraviruses may come from a "different tree of life altogether," than the three domains of life known to science as bacteria, single-celled micro-organisms known as archaea, and eukarya which includes fungi, plants and animals.

According to Gustavo Caetano-Anolles, a professor of bioinformatics at the University of Illinois who was not involved with the research but studies giant viruses, his theory is that they descended from a cell.

If true, "then we will have two kinds of ancestors—an ancestor that is shared between viruses and cells and an ancestor shared by all the cellular super kingdoms," he told AFP.

"The problem here is more from an evolutionary point of view. Where do these viruses come from?

"They are definitely part of something that we do not understand very well and that has the same complexity as cells."

It may be that viruses that make people sick are "part of a lineage that go rogue," he added.

Meanwhile, the majority of viruses may be good guys that sow genetic diversity among Earth's life forms.

"Perhaps viruses are spreading the wealth. It is a way that nature has devised to spread the wealth of genetic information," he said.

The French scientists said they are hopeful that the discovery will lead to funding more research into how these Pandoraviruses operate, which could inform future biotech and biomedical innovations.

"Our knowledge of biology as a whole and of the origin of life is still very incomplete," they said.

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Torbjorn_Larsson_OM
5 / 5 (1) Jul 18, 2013
A bit confusing. Megaviruses seems to come from eukaryotes. These viruses that are even larger seems to come from a 4th cellular domain, or perhaps simply the DNA LUCA basal lineage. Then they should be smaller, having been parasites for a longer time, one would think.

OTOH they confirm (either way) that the LUCA was complex and predict it had introns (as archaea and eukaryotes still have).
baudrunner
1 / 5 (2) Jul 18, 2013
These viruses are really only important in that they confirm that the mechanism(s) exist(s) which give(s) rise to viruses in the first place. There is no doubt that all life is descended from viruses, in that evolutionary advancements occur through their sexual reproduction (sexual reproduction being defined as the exchange of genetic information). It is important to understand this process of viral emergence, because therein lies the root to understanding life itself.
baudrunner
1 / 5 (1) Jul 18, 2013
One may argue that viruses need eukaryotes to reproduce or, rather, replicate. But are eukaryotes absolutely essential for this process? It may be possible that these immense viruses emerged from being densely packed together at some stage in their earliest paleontological history.
evolution3
not rated yet Jul 19, 2013
A bit confusing. Megaviruses seems to come from eukaryotes. These viruses that are even larger seems to come from a 4th cellular domain, or perhaps simply the DNA LUCA basal lineage. Then they should be smaller, having been parasites for a longer time, one would think.

OTOH they confirm (either way) that the LUCA was complex and predict it had introns (as archaea and eukaryotes still have).


Or those megaviruses are a relatively recent evolutionary sideline, which would explain why they are so big. The genome of them should be fully sequenced to find out which relation they have with other organisms, although it might get problematic because of al the lateral gene transfer.
evolution3
not rated yet Jul 19, 2013
One may argue that viruses need eukaryotes to reproduce or, rather, replicate. But are eukaryotes absolutely essential for this process? It may be possible that these immense viruses emerged from being densely packed together at some stage in their earliest paleontological history.


Well at least they need the metabolism and replicating machinery of "real" life forms. So there are two possibilities: 1) They descent from one or some of the existing domains and lost their ability to replicate themselves because of their lifestyle or 2) they are remnants of early life. Then there must've been a stage where all that is needed for their metabolism and replication must've been there in high concentraion close by.
Either way its a very interesting research and may lead to big discoveries and breakthroughs in evolutionary biology.

PS: I am very interested in what those proteins of unknown function are there for!
baudrunner
1 / 5 (1) Jul 19, 2013
PS: I am very interested in what those proteins of unknown function are there for!
They have no purpose. They are merely random aggregations of amino acids. Natural chemical synthesis processes give rise to them. Sadly (for some), there is no purpose to life other than to fulfill the requirement for consciousness to exist as a predisposition to the idea that begat the process of creation in the first place. So as it turns out, life evolved from random processes to complete that picture.

I'll turn it over to the religious nuts now.

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