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Largest Virus Ever Spawns from Amoebas

This has come as no surprise for researchers

Dec 9, 2009 08:39 GMT  ·  By
An amoeba containing Marseillevirus in (a) and (b), a Marseillevirus replicates itself in (c) and (d), while (e), (f) and (g) are reconstructions of electron micrographs of Marseillevirus
   An amoeba containing Marseillevirus in (a) and (b), a Marseillevirus replicates itself in (c) and (d), while (e), (f) and (g) are reconstructions of electron micrographs of Marseillevirus

Microbiologists keeping an eye on the world of viruses have recently discovered the largest such organism known. Dubbed Marseillevirus, the structure is in fact a mix-up of genetic bits and pieces, and is highly unlikely to hold on to its position as the world's largest virus for a very long time. Amoebas are known for their ability to produce incredibly large viruses, mostly because their internal structure allows for that to happen, Wired reports.

Amoebas are lowly, single-celled organisms, which spend their life consuming all food in their vicinity. Because of their massive appetite, they consume even things that would best be left outside a living cell. These abilities that the organisms have allow them to basically become an incubator for genetic remixing, creating viruses and other microorganisms that can become very dangerous. In fact, evolutionary biologists say, it may be that organisms such as amoebas allowed for the development of complex life back in the early days of our planet, by mixing chemicals that would have otherwise remained separated.

“What we find is that inside the amoeba, a virus can meet bacteria, archaea and prokaryotes. A whole new repertoire of an organism can be composed,” microbiologist Didier Raoult, from the Marseille, France-based University of the Mediterranean, explains. The expert is part of a group that spent several years studying the mimivirus, an organism so large, that the team thought at first that it was a microbe. After studying it, it became clear that it was in fact a virus, and one that could also be infected by other viruses, which was not thought possible before.

According to a scientific paper published on Monday in the latest issue of the journal Proceedings of the National Academy of Sciences (PNAS), the Marseillevirus is even larger than the mimivirus. “It’s 200 times bigger than the human genome. It’s a whole world in there,” the French expert says, speaking about the size of the amoeba genome. The microorganism has the largest genome in the world, scientists know. “We have this idea that everything is derived from something with very old roots. But there is still creativity going on, creating new origins,” Raoult says.

He adds that prokaryotic forerunners, which came before modern amoebas, might have, in fact, been the necessary incubators that allowed for the evolution of eukaryotic organisms.