Fantastical World of Potential Giant Viruses Lurks beneath Soil

One shape is dubbed “haircut” for its fibers that bristle like freshly buzzed hair. “Gorgon” has tubelike appendages snaking from its shell. And flaps poking out of “turtle” resemble the reptile’s head, limbs and tail, virologist Matthias Fischer and colleagues said, according to the Science News.

These and other peculiar-looking shapes “clearly tell us that we’ve underestimated how structurally diverse these viruses are,” says Fischer, of the Max Planck Institute for Medical Research in Heidelberg, Germany.

Since the discovery of the first giant virus in 2003, scientists collecting genetic material from the environment have uncovered a wide world of giant viruses (SN: 3/21/18). These viruses are roughly 10 to 50 times the diameter of viruses that cause the common cold. The genetic data suggest that giant viruses are diverse, widespread and abundant.

But genetics can’t tell us everything about a virus’s biology, says Steven Wilhelm, a microbiologist at the University of Tennessee in Knoxville. “We don’t know what we’re looking at, who it infects or what it could possibly be doing.”

The new work could help change that, Fischer says. Using transmission electron microscopy, his team analyzed about half a kilogram of soil from Harvard Forest in Petersham, Mass., to produce an image gallery of giant virus diversity — potentially.

Fischer is careful not to call the virus look-alikes “viruses” just yet. The researchers have seen the particles only with a microscope; they haven’t confirmed that the potential viruses can infect particular organisms.

Still, looking at the structures Fischer’s team identified, microbiologist Frederik Schulz of the Joint Genome Institute in Berkeley, Calif., says he’s “convinced that many of these are actual virus particles.”

Scientists can only speculate why giant viruses might form tubular, bristly or turtlelike appendages. They may help the virus infect a host or perhaps move through the environment, Fischer says. “It’s going to be a wild ride … to see what each of these structures do.”

Whatever function they may have, Fischer thinks even more peculiar shapes remain to be discovered. “If a handful of forest soil already contains so many different virus particles,” he says, “this is clearly just the very tip of the viral Mount Everest.”

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