Professor Jean-Michel Claverie and Dr. Chantal Aberge of the French University of Aix-Marseille (Aix-Marseille Université) have discovered the largest viruses in the world, that have been called Pandoravirus. They have found two species, the Pandoravirus salinus, that lives in the saline water near the mouth of the Chilean river Tunquen, and the Pandoravirus dulcis, that lives in a freshwater pond near Melbourne, Australia.

Their size, a micrometer, meaning a thousandth of a millimeter, may seem very little but for a virus that’s huge, so much that it’s comparable to that of a bacterium. Its appearance is also more similar to that of a bacterium that to a normal virus. The Pandoravirus salinus has about 2,500 genes, really a lot if you think that the influence virus has only 13 genes.

Previously, the world’s largest virus was the Megavirus (photo ©Chantal Abergel), isolated in April 2010 again by Professor Jean-Michel Claverie and Dr. Chantal Aberge. It’s estimated that this virus has about 1,120 genes and its diameter is 440 nanometers. It’s a giant among viruses but it’s small compared to the Pandoraviruses.

As if the Pandoraviruses weren’t already strange enough, according to the first genetic analysis performed on their DNA it seems that they have less than 10% in common with other viruses or other life forms. If confirmed by further analysis, this result raises the question of their origin.

According to Professor Jean-Michel Claverie, the Pandoraviruses might be the survivors of a type of ancestral cells that no longer exist today. Over time, it’s possible that those cells have become parasites to survive, infecting especially the amoebae. Probably, the amoebae mistake the Pandoraviruses for bacteria and try to eat them only to be infected by them.

The opinions about viruses are very different among biologists. If you want to start a brawl among biologists, simply gather a group of them and ask them whether viruses are alive or not. With regard to the Pandoraviruses, differing opinions from various biologists have already arrived so there are those who disagree with Professor Jean-Michel Claverie concerning their origin.

It’s a fact that in recent years giant viruses have been discovered, this because in the past nobody looked for them thinking that viruses were all very small. The recent years discoveries are changing this way of thinking. Obviously, more research and in-depth analysis of the Pandoraviruses DNA must be done and considering this new interest from the biologists we can expect new surprises.

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