Megavirus face to face with its runner-up in size, the Mimivirus. Top view is the early stage of the viruses, while the bottom view shows the mature virion factories in full production. (c) PNAS

A few days ago I reported how researchers found a myriad of new virus strains inside raw sewage. On a related, more intriguing, note French scientists have recently discovered the largest virus ever discovered so far in the ocean waters off the coast of Chile. Scientists estimate it’s between 10 and 20 times the size of an average virus.

Dubbed Megavirus, and just a tad larger than the previous record-holder, the Mimivirus, the virus is the biggest one in the world scientists have managed to find so far, showcasing a linear double-stranded DNA molecule with 1,259,197 base pairs. Due to its size, the Megavirus has a complex genome which grants it certain abilities, like the protein translation, that overlap with simple cellular organisms like parasitic bacteria or DNA-repair enzymes, which allow it to correct damage due to ultraviolet light, radiation or chemicals. In fact, it’s so large that it can be seen with a typical light microscope rather than an electron microscope.

The giant virus, 0.7 micrometers in diameter, prefers the single-celled amoebas that live in the water as its host, invading the cell by means of a Stargate structure. Yes, that’s really the coined term. Viruses cannot copy themselves but must invade a host to replicate, and Megavirus has over 1,000 genes carrying the instructions to replicate itself once inside its host, the researchers said.

“Everything is initiated from a single particle, and then grows and grows to become this virion factory,” Claverie said. “That’s why it needs all these genes.”

Though it’s the biggest virus in the world, scientists assure us that it posses absolutely no threat to human organisms, and only affects single cellular organisms in the water.

The study was reported in the journal PNAS.