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Scientists' first discovery of a viral nemesis! Do natural enemies of viruses really exist?

Mengyan Yu

About “virovore”

We already know an organism classification by food source: Carnivore-animals that feed on meat, and Herbivore-animals that feed on plants. Recently, scientists may have discovered the first organism that feeds exclusively on viruses and have added a new category to the classification of the organisms: virovore, which have a virus-only diet. The results of the research were written up in the paper and published in the Proceedings of the National Academy of Sciences (NAS).

This new finding not only fills the gap in food chains and overturns the viral shunt hypothesis, it also revolutionizes human cognition of viruses and the ecological model of existing perceptions, and even influences people’s opinions on global carbon cycling.

A ciliate, or cilia-propelled microorganism, belonging to the genus Halteria. New research led by Nebraska’s John DeLong has revealed that ciliates can feed on water-dwelling viruses — and even grow on a virus-only diet.

From: Proyecto Agua via flickr (CC BY-NC-SA 2.0)


How did scientists find out virovore Virovore

Discussing how did scientists find out virovore, it was actually due to the obsession with “balance” and “integrity” of the researchers. In the existing cognition, it seems that the rampaging viruses have never appeared in the food chain of the dog-eat-dog world. “Viruses are made up of nucleic acids, a lot of nitrogen and phosphorous,” said John DeLong, one of the paper’s authors. “Surely everything should want to eat them.”

Earlier in 1993, Canadian scientist Curtis Suttle had already done some experiments finding that single-celled protists were capable of consuming and digesting viruses, but delved no further to prove it whether deliberately. But professor Suttle always believes the virovore may exist. Recently, John’s research team was studying the chlorovirus (a virus that widely separates in water and often gains access to green algae), and by coincidence, the team inadvertently came up with the hypothesis: do these microorganisms living in water feed specifically on viruses to produce the energy they need itself?

Most organisms may accidentally feed on viruses, but John said he want to see if any organisms would feed exclusively. Further research was then undertaken by the team to find out the query.


Experiments and results

To test the proposed hypothesis, the researchers of John’s team drove out to a nearby pond and collected some water samples containing a large number of microorganisms. Next, they added generous portions of chlorovirus to one sample, and the other keep the original. To confirm that the microorganisms were actually consuming the virus, the team tagged some of the chlorovirus DNA with a fluorescent green dye before it was introduced to the two types of plankton to figure out how the food chain works.

Researchers have discovered that a microbe called "Halteria" frantically devours the virus and thrives. In the water samples that did not contain other food sources, the population of the Halteria was growing an average of about 15 times larger over that same timespan and the number of chloroviruses was plummeting by as much as 100-fold in just two days. Halteria deprived of the chlorovirus, meanwhile, wasn’t growing at all. Paramecium also acts the same. It also used chlorovirus as a source of nutrition. Moreover, this confirmed that viruses were being eaten: the Halteria’s vacuoles – microbial equivalent of stomachs – were glowing green from the feeding, and the fluorescent green mobile traces marked on the chlorovirus DNA.

The microbe Halteria is a common genus of protists known to flit about as its hair-like cilia propel it through the water, this kind of ciliate actively feeds on viruses. Some ciliates are only about 100 microns in size, and they may likely be able to sustain growth if enough virus is consumed. Paramecium, On the other hand, is a kind of grass crawler.

This suggests that two planktonic organisms, Halteria and Paramecium, can actively eat viruses and thrive. But the differences between these two is that while the Paramecium snacked on the viruses, its sizes and numbers barely budged so it cannot be considered as a virovore. Whereas Halteria, on the other hand, their numbers grew rapidly in just two days. They dined on them, using the chlorovirus as a source of nutrients, they digest and absorb them and ultimately can grow also reproduce normally. So they are the real virovore.

Halteria feeds on the Chlorovirus and absorbs viral nutrients to grow

From: a-world-first


A profound finding

According to the above experiments, the researchers finally confirmed that the protozoan Halteria is the first organism discovered by humans to feed on viruses! This discovery is certainly disruptive for biological academia. One of the important breakthroughs was the rejection of the viral shunt hypothesis, which showed that viruses do not completely block the movement of the energy and materials from bacteria up toward the food chain. But are instead consumed by the protists, which continues the flow of energy and materials up toward the food chain. This suggests that the viral shunt hypothesis no longer applies.

Perhaps in the near future, humans will be able to discover more virovore. Even further, during the studies of virovore, we may find new ways of fighting and eliminating viruses. The researchers indicate that after that they will continue to focus on these questions: How might it shape the structure of food webs? The evolution and diversity of species within them?

Maybe, mankind will defeat viruses and get rid of diseases through continues research…


Reference reproduction-of-microorganism/ been-found-in-a-world-first

A ciliate, or cilia-propelled microorganism, belonging to the genus Halteria. New research led by Nebraska’s John DeLong has revealed that ciliates can feed on water-dwelling viruses — and even grow on a virus-only diet.

From: Proyecto Agua via flickr (CC BY-NC-SA 2.0)

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