Gigantic Giant Viruses and the Endless Viral Frontier

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Pandoravirus. Photo by Chantal Abergel and Jean-Michel Claverie

In my column this week for the New York Times, I write about the discovery of record-breaking viruses called pandoraviruses. They’re 1000 times bigger than a flu virus and have almost 200 times as many genes–over 2500. That’s twice as many genes as the previous giant-virus record holder, which I blogged about in 2011.

These giant viruses are important to our understanding of what the difference is–if any–between viruses and the rest of life. But they’re also part of a bigger story, one that inspired the title of my recent book A Planet of Viruses. Viruses are the most common life form on Earth, they are by far the most genetically diverse, and we have barely started to explore the viral frontier.

That frontier includes giant viruses–and tiny ones, too. Just last week, for example, Jessica Labonte and Curtis Suttle of the University of British Columbia published a survey of another group of viruses called single-stranded DNA viruses. Their ranks include parvoviruses, which cause an infection sometimes known as the Fifth Disease. If you’ve gotten it, like I did a few years ago, you know that feeling it provides you that someone has been using your body as a punching bag for hours.

The ranks of single stranded DNA viruses include many other pathogens of plants and animals, plus others that infect bacteria. They are exquisitely small, with as few as three genes.

Labonte and Suttle searched through sequenced of DNA that have been trawled up from sea water at a few sites around the world. They found a lot of single-stranded DNA virus genes, which they compared to the seven known families of the viruses. They realized they have probably discovered 129 new families.

Just another week on the viral frontier…