Jumping DNA rides aboard a virus, which infects a giant virus, which infects an amoeba, which infected a woman’s eye …

Earlier this year, a 17-year-old French woman arrived at her ophthalmologist with pain and redness in her left eye. She woman had been using tap water to dilute the cleaning solution for her contact lenses, and even though they were meant to be replaced every month, she would wear them for three. As a result, the fluid in her contact lens case had become contaminated with three species of bacteria, an amoeba called Acanthamoeba polyphaga that can caused inflamed eyes.

The mystery of the womans inflamed eyes was solved, but Bernard La Scola and Christelle Desnues looked inside the amoeba, they found more surprises.

It was carrying two species of bacteria, and a giant virus that no one had seen beforethey called it Lentille virus. Inside that, they found a virophagean virus that infects other viruseswhich they called Sputnik 2. And in both Lentille virus and Sputnik 2, they found even smaller genetic parasites tiny chunks of DNA that can hop around the genomes of the virus, and stow away inside the virophage. They called these transpovirons.

So, the poor red eyes of the French patient were carrying an entire world of parasites, nested within one another like Russian Matryoshka nesting dolls. The transpovirons were hidden in the virophage, which infected the giant virus, which infected the amoeba, which infected the womans eyes.

Rise of the virophages

The same team found the first virophage Sputnik back in 2008, under similar circumstances. In dirty water from a Parisian cooling tower, they had isolated an amoeba that contained a new giant virus mamavirus which was infected by Sputnik (named after the Russian for fellow traveller). Mamavirus a virus as big as some bacteria creates large viral factories inside the amoeba, where it makes new copies of itself. Sputnik hijacks these factories to replicate itself at mamavirus expense. It was a groundbreaking discoveryproof that viruses themselves can get sick. Just as they infect cells, virophages can infect them.

The world of virophages continued to grow. Last year, Matthias Fischer and Curtis Suttle discovered a second one Mavirus inside another giant virus called CroV. Weeks later, Sheree Yau announced a third virophage OLV infecting the giant viruses of Antarcticas Organic Lake. Yau also searched through genetic databases for sequences that looked like OLV, and found matches from the Galapagos Islands, Panama, the USA and elsewhere in Antarctica. An entire world of virophages lay waiting to be found.

In Sputnik 2, La Scola and Desnues have discovered the fourth virophage. More importantly, they found its DNA inside that of its Lentille virus host. This proves that, just as other viruses such as HIV and herpes can insert their DNA into animal genomes, Sputnik 2 can insert its DNA into viral ones. This could explain why distantly related giant viruses often carry similar genes. By hopping in and out of their genomes, virophages could be acting as vehicles that transfer genes from one giant virus to another.

Transpovirons

Next, the team did scoured the DNA they recovered from Lentille virus for fragments that didnt belong into either Lentilles or Sputnik 2s genomes. Its a process that team leader Didier Raoult describes as looking in the trash. He says, If you want to see something really bizarre, you have to look where you didnt know to look in the first place. And he was right.

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Jumping DNA rides aboard a virus, which infects a giant virus, which infects an amoeba, which infected a woman’s eye ...