Genetic loot transformed little viruses into giants

by Giorgia Guglielmi

Giant viruses are the sperm whales of the microscopic world, dozens of times larger than typical viruses. They’re also richer in genes and much more complex—so much so, in fact, that scientists have speculated whether they evolved from ancient single-celled organisms. But the discovery of a novel group of giant viruses, reported today in Science, indicates that was likely not the case. These mammoth viruses, named Klosneuviruses, started out similar in size to their tiny, simpler brethren, and increased in complexity by gradually pilfering genes from the cells they infected. Compared to other known viruses, the newfound giants contain a more complete set of molecules able to translate genetic instructions into proteins. The researchers found that the genes that produce these protein-making molecules do not derive from an individual organism but rather from several single-celled algae—Klosneuviruses’ favorite hosts. This suggests that, over the course of evolution, Klosneuviruses—and probably other giant viruses—repeatedly gained new genes from the cells they took over. Over billions of years, this genetic larceny turned them into something unique: a cell-like virus that straddles the line between living and non-living.

 

Publication: Frederik Schulz, Natalya Yutin, Natalia N. Ivanova, Davi R. Ortega, Tae Kwon Lee, Julia Vierheilig, Holger Daims, Matthias Horn, Michael Wagner, Grant J. Jensen, Nikos C. Kyrpides, Eugene V. Koonin, Tanja Woyke. Giant viruses with an expanded complement of translation system components. Science, 2017; 356 (6333): 82 http://science.sciencemag.org/content/356/6333/82

 

Electron microscope photograph of a Megavirus, a giant virus similar to those that have just been discovered.
Image credits: Chantal Abergel (CC BY-SA 3.0)

 

Giorgia Guglielmi is a graduate student in the MIT Program in Science Writing and a freelance science journalist based in Cambridge, MA. She received a PhD in Biology from the European Molecular Biology Laboratory in Heidelberg, Germany, where she studied how embryos get their final shape

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