Found: Largest virus ever

Researchers have discovered the world's largest virus, which has 112 times the number of genes of the average flu virus.

Mimivirus and Mamavirus, say hello to Megavirus.

One of a new class of giant viruses discovered, Megavirus is the world's largest, clocking in with a genome that is 1.259 million base pairs long, 6.5% larger than the previous record holder.

Its abundance of DNA holds 1,120 genes. In contrast, the average flu virus has 10 genes.

Even in diameter, it is 10 to 20 times wider than the average virus and can be seen with a regular light microscope rather than an electron microscope.

So, you get the picture. It's big.

Megavirus was discovered after a giant ocean trawl for interesting biology by a team of scientists led by Jean-Michel Claverie of Aix-Marseille University in Marseille, France. They announced their findings this week in the Proceedings of the National Academy of Sciences. You can browse the genome here.

How it lives

Megavirus lives similarly to its relative, Mimivirus, the second-largest virus: Both infect amoebas (not humans), and both invade host cells using a five-pronged stargate structure that then initiates the release of the virus’ genetic material.

Actually, the scientists used the fact that Mimivirus infects amoebas to discover Megavirus. The researchers took three types of amoebas, exposed them to different samples of water and waited to see if any viruses grew in them. A sample of water from Chile and an amoeba gave birth to Megavirus, whose full scientific name is Megavirus Chilensis.

Where it comes from

Giant viruses like Megavirus are intriguing to scientists because of the mystery of their origin. As reported in Wired, their genomes carry a lot of genes that replace basic cellular functions, such as those involved in DNA repair and protein manufacturing. That led one scientist to propose that viruses may explain DNA-based life. Other scientists surmise that these viruses stole those genes from cells they infected.

However, the structure of Megavirus, especially when compared with Mimivirus, now leads the authors to believe that the giant viruses descend evolutionarily from an ancient, free-living eukaryotic cell. As it evolved, it lost various genes and structures, leaving its current form: something that propagates grows like a virus, but has a separate lineage from all other known viruses.

Photo: Megavirus particle (Chantal Abergel/Wikimedia Commons)

via: Popular Science, CBS News, Wired, Proceedings of the National Academy of Sciences

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