SINGLE-CELLED MARINE PROTISTS FOUND TO DEVOUR VIRUSES

Teeny, single-cell creatures floating in the ocean may be the first organisms ever confirmed to eat viruses. Scientists scooped up the organisms, known as protists, from the surface waters of the Gulf of Maine and the Mediterranean Sea off the coast of Catalonia, Spain.

They found a slew of viral DNA associated with two diverse groups of protists, called choanozoans and picozoans; the same DNA sequences cropped up in many members of the two groups, despite some of these single-cell organisms not being closely related.

"It would be like organisms as distantly related as trees and humans, or even more distantly related than that," said lead author Julia Brown, a bioinformatician at the Bigelow Laboratory for Ocean Sciences in Maine. "It's very, very unlikely that those viruses are capable of infecting all the organisms we found them in," Nicoletta Lanese wrote for LiveScience on September 24, 2020 (September 25, 2020 in Manila.) After running a number of tests, Brown and her colleagues concluded that the protists likely consumed the viruses as food, rather than picking them up by chance or being infected by them. The team says their findings, published online on September 24 in the journal Frontiers in Microbiology, could reshape how we think about the entire ocean food web, the network of who-eats-who that connects everything from tiny bacteria to plants to blue whales.

However, one expert told Live Science that the study doesn't conclusively prove that the protists actually ate the viruses. "The detection of viral sequences in ... cells alone can hardly answer the question of how these virus particles entered the cell," Christian Griebler, a freshwater microbial ecologist at the University of Vienna, who was not involved in the study, said in an email. More work will be needed to show how and whether these protists gobble up viruses, and if so, how much nutrition they gain from these microscopic snacks, he said.

While choanozoans are known to consume bacteria, the diet of picozoans remains somewhat mysterious. One report, published in 2007 in the journal PLOS ONE, found that the picozoa feeding apparatus is too small to capture bacterial cells, but large enough to engulf particles less than 0.000006 inches (150 nanometers) in diameter, which could include viruses. "Picozoa are a really mysterious group of protists in the ocean," Ramunas Stepanauskas, a senior research scientist at the Bigelow Laboratory for Ocean Sciences, told Live Science.

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