The very first giant virus was discovered in a water-cooling tower in 2003. As the name suggests, giant viruses are unusually large and their genomes unusually complex, all of which went against the prevailing idea of viruses as small, simple, and primitive. Then one baffling giant virus became many, as scientists kept discovering different types: in water off the Chilean coast, in Siberian permafrost, in an Austrian sewage plant, and now in mud from a Japanese hot spring.
The newest giant virus is Medusavirus, so named because of the way it infects amoebas, single-celled organisms that commonly live in water. When Masaharu Takemura, a virologist at Tokyo University of Science, first grew microbes from the hot-spring mud in his lab, he noticed that some amoebas would die in the presence of the giant virus. The dead amoeba cells burst open. But others would shrivel and harden, which amoebas sometimes do when guarding against bacteria that also prey on them. (It’s a dangerous life out there for amoebas.)
Takemura told me in an email that he had long been fascinated with the myth of Medusa, who turned men who looked at her to stone. His computer background is Peter Paul Rubens’s famous painting of Medusa. Thus inspired, he named the new giant virus Medusavirus.
Takemura and his colleagues then analyzed the new virus more closely. They put it under an electron microscope and found that it resembles a 20-sided die, covered in 2,660 round-tipped spikes. It’s unclear exactly what the purpose of the spikes are, but they have been found in other giant viruses. The team sequenced the virus’s DNA, which revealed the most interesting information of all.