For the first time, scientists discover organisms whose diet relies on eating viruses

Humanity loves a good villain, and few villains are as menacing and sinister as a virus. They are virtually invisible, a brutal parasite that hijacks our own living cells, turning their biological essence into more viral soldiers to continue the slaughter.

But viruses play an extremely important role in the ecosystem. They are like the apex predators of the savannah, the lions that control gazelle populations by reducing their numbers.

This is the first time that it has been shown that a viral-only diet can be enough for the survival of a microorganism, a practice that researchers call “viroviry”, i.e. feeding on viruses. .

For example, sometimes simple aquatic plants called algae will begin to reproduce uncontrollably, causing a algae bloom. Some flowers can be poisonous, smother beaches or lakes and smother wildlife, often swelling so large they can be seen from space. Blooms can occur naturally, but various human activities, such as nutrient pollution from agricultural runoff or sewage discharges, can trigger a bloom or make it worse.

Next come the chloroviruses. Named after the Greek word meaning “green”, it is a large species of virus found all over the world in freshwater environments. And they love to infect algae. Chloroviruses actually play an important role in controlling algal blooms.

However, when a virus kills an algae cell, bursting it like a wet balloon, all those nutrients hidden inside are released into the water, where they are sucked up by other microbes. This is called the “viral shunt” and it means that other organisms higher up the food chain do not benefit from this nutrient cycle.

They found that Halteria sp. not only greedily devoured the viruses, but they had enough nutritional value to thrive and reproduce.

However, new research in the journal Proceedings of the National Academy of Sciences provides evidence that not only are chloroviruses regularly consumed, but that they are also nutritious, which has broad implications for how we think about food chains and the Earth’s carbon cycle. The paper was co-authored by a professor of plant pathology James Van Etten, who discovered for the first time chlorovirus in 1980.

To study this, researchers at the University of Nebraska-Lincoln collected pond water containing a microbe called Halteria sp. These tiny creatures are called ciliates because they are covered in tiny hair-like projections called cilia. Then they fed the ciliates heaped portions of chlorovirus, with some cultures feeding nothing to serve as controls.

They found that Halteria sp. not only greedily devoured the viruses, but they had enough nutritional value to thrive and reproduce. To really prove that it was happening, they labeled the viruses’ DNA with a fluorescent green dye. And when they checked the “stomachs” of these microbes (technically called the vaculole), they found glowing viruses inside. This is the first time that it has been shown that a viral-only diet can be enough for the survival of a microorganism, a practice that researchers call “viroviry”, i.e. feeding on viruses. .

“If you multiply a crude estimate of the number of viruses, the number of ciliates, and the amount of water, it gives this massive amount of energy movement (up the food chain),” the lead author said. of the study, John DeLong. , an associate professor at the University of Nebraska-Lincoln, said in a statement. He and his colleagues estimate that ciliates in a small pond could eat 10 trillion viruses per day. “If this happens on the scale that we think it could be, it should completely change our view of the global carbon cycle,” DeLong said.


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Indeed, this is a relationship that is sorely lacking in food chain models. The authors claim that “current food web models lack a critical interaction”, but there is surprisingly little research in this area.

“I was motivated to figure out if it was weird or not, or if it was okay,” DeLong said. “It’s not weird. It’s just that no one noticed.”

To learn more, DeLong wants to repeat this experiment outside the lab. The discovery of the first vivorore is really underlined how little we know about the microbes around us, not to mention their evolution. Creatures that eat viruses will put selective pressure on them, which over time will change their genetics. Not only does understanding this relationship have big implications for how nutrients are cycled through the ecosystem, it illuminates some of the fundamental mechanisms of life itself.

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