Introducing the Virophage, or the virus which infects other viruses.

[Eric P]

http://scienceblogs.com/notrocketscience/2008/08/the_virophage_a_virus_that_infects_other_viruses.php

The virophage - a virus that infects other viruses

Category: Parasites • Viruses
Posted on: August 7, 2008 5:41 AM, by Ed Yong

Blogging on Peer-Reviewed ResearchViruses may cause disease but some can fall ill themselves. For the first time, a group of scientists have discovered a virus that targets other viruses. This new virus-of-viruses was discovered by Bernard La Scola and Christelle Desnues at the University of the Mediterranean, who have playfully named it Sputnik, after the Russian for "fellow traveller". It is so unique that they have classified it in an entirely new family - the "virophages" - in honour of the similarities it shares with the bacteriophage viruses that use bacteria as hosts.

Viralcapsid.jpgThe story of Sputnik started in 1992 with some dirty English water. A group of scientists were studying an amoeba taken from a cooling tower in Bradford, England, when they discovered a microscopic giant - a virus so large that it was originally mistaken for bacterium. It was only in 2003 that La Scola and colleagues conclusively showed that the new find was indeed a virus. But what a virus - APMV, or 'mimivirus', measures a whopping 400 nanometres across.

The search for giant viruses continued. La Scola's team identified another strain of APMV by inoculating the same species of amoeba with water taken from another cooling tower, this time from Paris. The new specimen seemed to eclipse even the original giant in size, and the researchers decided to call it 'mamavirus'.

When this record-breaker infects amoebae, it forms gigantic viral factories that pump out new copies of itself. When the team looked at these under an electron microscope, they found the equivalent of microscopic Russian dolls - tiny viral particles, just 50 nanometes in size and distinct from mamavirus itself. It's all very meta, and to the researchers, the fact that mamaviruses can "get sick" themselves is further evidence that viruses are indeed living things.

Metavirus

Sputnik.jpg La Scola and Desnues found that Sputnik couldn't multiply within the amoeba by itself; it could only spread within cells that had also been infected with mamavirus. But Sputnik is no partner - by hijacking the mamavirus's replication machinery, it spreads at the expense of its larger host and substantially hinders its reproduction. In the presence of the tiny intruder, mamavirus particles assemble abnormally and surround themselves with unusually thick outer coats. As a result, their ability to infect the amoeba fell by 70%.

The virophage name is perhaps a bit misleading. Bacteriophages reproduce within the cells of bacteria, whereas Sputnik is a satellite virus, in more than name only. Like hepatitis D, it depends on another virus coinfecting a host in order to spread. But it's the fact that it does so at the expense of the mamavirus that makes it a true parasite.

In comparison to its sizeable host, Sputnik is tiny and sports a genome that is almost a hundred times smaller. Its 18,000 base-pairs of DNA contains just 21 genes and when La Scola and Desnues analysed these, they found that Sputnik is a genetic chimera - a mish-mash of different genes from different sources. Thirteen of these have no equivalent in any other known virus, while the remainder have similarities to genes from other viruses, bacteria and even more complex cells.

Three of these are closely related to mamavirus genes, suggesting that this tiniest of parasites has been raiding genetic material from its host and from other viruses. La Scola and Desnues even suggest that Sputnik could be acting as a genetic mule, shuffling genes between giant viruses. It could even explain why mimivirus has mysteriously and recently picked up bacterial genes of unknown origin.

Reference: Nature doi:10.1038/nature07218

[bagofeyes]

are we invincible now?

[Eric P]

not yet.

my girlfriend works for Nature, where the article is now live, so i'm going to see if she can sneak me the full paper/report

[The Fake Shemp]

This how every bad horror movie starts.

USE A VIRUS TO ATTACK ANOTHER VIRUS OH NOES ITS MUTATED!

[Eric P]

well this is rather more limited in scope.

so far, from what i'm reading, this has only been able to force infection into a specific virus.

Viruses are obligate parasites of Eukarya, Archaea and Bacteria.
Acanthamoeba polyphaga mimivirus (APMV) is the largest known
virus; it grows only in amoeba and is visible under the optical
microscope. Mimivirus possesses a 1,185-kilobase double-stranded
linear chromosome whose coding capacity is greater than that of
numerous bacteria and archaea1–3. Here we describe an icosahedral
small virus, Sputnik, 50nm in size, found associated with a new
strain of APMV. Sputnik cannot multiply in Acanthamoeba castellanii
but grows rapidly, after an eclipse phase, in the giant virus
factory found in amoebae co-infected withAPMV4. Sputnik growth
is deleterious to APMV and results in the production of abortive
forms and abnormal capsid assembly of the host virus. The Sputnik
genome is an 18.343-kilobase circular double-stranded DNA and
contains genes that are linked to viruses infecting each of the three
domains of life Eukarya, Archaea and Bacteria. Of the 21 predicted
protein-coding genes, eight encode proteins with detectable homologues,
including three proteins apparently derived from APMV, a
homologue of an archaeal virus integrase, a predicted primase–
helicase, a packaging ATPase with homologues in bacteriophages
and eukaryotic viruses, a distant homologue of bacterial insertion
sequence transposase DNA-binding subunit, and a Zn-ribbon protein.
The closest homologues of the last four of these proteins were
detected in the Global Ocean Survey environmental data set5, suggesting
that Sputnik represents a currently unknown family of
viruses. Considering its functional analogy with bacteriophages,
we classify this virus as a virophage. The virophage could be a
vehicle mediating lateral gene transfer between giant viruses.

and also this is kind of awesome

Sputnik did not multiply when inoculated into A. castellanii
(Supplementary Information and Supplementary Table 4).
However, this virus did grow, as demonstrated by transmission electron
microscopy and polymerase chain reaction, in A. castellanii coinfected
with mimivirus or mamavirus...

it didn't reproduce, but rather grew larger.

[The Fake Shemp]

If you get the full report, please share.  Microbiology, especially virology, gives me a boner.  I even read the bad Richard Preston stuff.

[Tauntaun]

This how every bad horror movie starts.

USE A VIRUS TO ATTACK ANOTHER VIRUS OH NOES ITS MUTATED!

Seriously, this is the beginning of zombie apocalypse.

[Eel O'Brian]

don't be so negative, perhaps we'll all get superpowers

[Tauntaun]

don't be so negative, perhaps we'll all get superpowers

Or maybe just a select few of us, it's no fun if everyone has it.

[Eel O'Brian]

maybe some of us get the powers, and the rest become zombies

[Tauntaun]

maybe some of us get the powers, and the rest become zombies

That works, but we should have a few people who aren't effected at all and we have to protect them from the zombies.

[Crushed]

I read about this in a Discover a few years ago. They wondered if these huge viruses may have had some kind of part in evolution.

Nothing to fear here people, they are like gentle virus whales defending us from the evil virus sharks.

[xnikki118x]

If you get the full report, please share.  Microbiology, especially virology, gives me a boner.  I even read the bad Richard Preston stuff.

Same here man. Not so much interest in virology, but micro and marine.

[MrAngryFace]

Well if the gigantic collider doesnt create a black hole, we'll turn ourselves into the undead.

[Joe Molotov]

If you get the full report, please share.  Microbiology, especially virology, gives me a boner.  I even read the bad Richard Preston stuff.

Virofag

[Cormacaroni]

Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum.

[TVC15]

This how every bad horror movie starts.

USE A VIRUS TO ATTACK ANOTHER VIRUS OH NOES ITS MUTATED!

And now there is a plausible reason to make ID4-2

[laesperanzapaz]

Richard preston, people who make money off of hyperbolizing reality

[Mupepe]

I Am Legend?

[JustinP]

i'll do it if it gives me superpowers.