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Microorganisms: The Pandoravirus

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1101242.  Mon Nov 10, 2014 11:40 pm Reply with quote

Challenging Standard Viral Evolutionary Models

Named due to the as yet unknown consequences of its discovery, ‘Pandoravirus’ denotes a genus of extremely large viruses, and has the largest genomes of any viral genus. This makes it the largest virus in (discovered) existence. Like other very large viruses (such as Mimivirus, Pithovirus and Megavirus), Pandoraviruses infect amoebas. Pandoravirus’ genome is roughly twice the size of Megavirus, the next biggest virus in existence. (Although the capsid (the protein- based shell around a virus) of Pithovirus is roughly 50% larger in size, it does not have a larger genome than Pandoravirus.) While other viruses range between 50- 100 nanometres in size, Pandoraviruses are roughly one micron (one thousandth of a millimetre in length). They contain roughly 2,500 genes each. To put this into perspective, common viruses such as the flu or AIDS contain around 10 genes each.

Pandoraviruses’ Discovery
Pandoravirus was discovered by a team of French scientists, led by the husband and wife team, Jean-Michel Claverie and Chantal Abergel, and first reported in the journal Science in July 2013. They found the virus, thought to be roughly 300,000 years old, embedded in Siberian permafrost.

Though other scientists had observed similar particles, they did not hypothesise that these particles might belong to a virus, owing to their size.

The first reported discovery of Pandoravirus was made by Patrick Scheid, a parasitologist from the Central Institute of the Bundeswehr Medical Service in Koblenz, Germany. He found an infected amoeba in the contact lens of a woman with keratitis.

Two separate Pandoravirus strains have since been found; one since named Pandoravirus salinus in saltwater, off of the coast of Chile, and one named Pandoravirus dulcis, found in a shallow freshwater pond at Latrobe University, in Melbourne, Australia. The fact that the virus has been found so far apart seems to indicate that the virus is not uncommon.

Time Magazine reported that according to Chantal Abergel, one of the authors of the new study, when scientists first discovered giant viruses they were so baffled that they simply tagged them NLF, that is, "New Life Form."

How Do They Differ to Other Viruses?
Firstly, the virus reproduces differently than the vast majority of other viruses. While most viruses create a new cell by building an empty ‘box’, and then filling it up with DNA gradually, Pandoraviruses do both of these processes at the same time- an activity scientists refer to as ‘knitting’.

Additionally, Pandoraviruses do not have a gene allowing them to build a protein like the capsid protein, which scientists consider to be a basic building block of traditional virus structures.

Most interestingly, only 6% of the proteins encoded by Pandoravirus are similar to those already identified in other viruses/ cellular organisms. The other 94% of Pandoraviruses’ 2,500 genes “cannot be traced to any known lineage in nature. In other words, they are completely alien to us.” Some scientists suggest that such foreign genes is evidence for the "controversial existence of a fourth domain of life” in addition to the three previously recognized: bacteria, archaea (formerly grouped together as prokaryotae) and eukaryotae to which humans also belong. Many scientists maintain that the three-domain system is "probably pretty wrong—we are missing some part of the puzzle here."

Jean-Michel Claverie and Chantal Abergel, two of the lead researchers who discovered the Pandoravirus, have stated that they have virtually no ideas as to what the functions of the newly discovered virus could be. “It is very possible that these unique genes could have functions that we have never seen before in other cells,” Abergel said. “Some genes resemble genes that we already know. For the others, we don’t have any clue about their function.”

Pertinent Information
Most importantly, scientists strongly believe that Pandoraviruses aren’t harmful to people, as most viruses simply infect other microbes.

This does, however, open uncertain scientific doors. Despite the virus being found in suspended animation, its revival in a laboratory stands as “a proof of principle that we could eventually resurrect active infectious viruses from different periods,” said the study’s lead author, microbiologist Jean-Michel Claverie of Aix-Marseille University in France. “We know that those non-dangerous viruses are alive there, which probably is telling us that the dangerous kind that may infect humans and animals -- that we think were eradicated from the surface of Earth -- are actually still present and eventually viable, in the ground,” Claverie said.

Though at this point this is speculation, scientists foresee many Pandoraviruses and similar marine viruses having a beneficial and unseen role in nature. For example, “viruses prey on and thus regulate a lot of the ocean's phytoplankton, which produces half of our planet's oxygen and forms the base of the ocean's food chain”.

Overall, it seems, the discovery of Pandoraviruses "demonstrates our shallow knowledge of microbiology on Earth."

-,0,4662287.story#ixzz2uvwls53Y, accessed 11.11.2014.
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- Nadège Philippe, Matthieu Legendre, Gabriel Doutre et al. (July 2013)."Pandoraviruses: Amoeba Viruses with Genomes Up to 2.5 Mb Reaching That of Parasitic Eukaryotes". Science 341 (6143): 281–6.Bibcode:2013Sci...341..281P. doi:10.1126/science.1239181.PMID 23869018.
- Yong, Ed (3 March 2014). "Giant virus resurrected from 30,000-year-old ice : Nature News & Comment". Nature. doi:10.1038/nature.2014.14801

*Please feel free to contact me for the original text, which includes footnotes in their original positions!


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