This organism only eats viruses, and that’s a big first

The discovery of the first organism capable of surviving by eating only viruses could have huge implications in several areas.

From bacteria to the largest mammals, including green plants, fungi, and every other organism, no matter what kingdom you’re interested in, there are bound to be others who have developed tools to eat them. At this level, viruses are exceptions; there are certain organisms that can attack them, but no one has yet described an organism.” viable “, that is, who lives exclusively on viruses.

This shortage puzzle specialists for several reasons. The first is that viruses are very abundant; even in a perfectly healthy little pond there are millions of virus particles capable of infecting a wide variety of hosts. It is therefore surprising to find no one who has chosen this diet.

And this inconsistency has become almost an obsession for John DeLong, a microbiologist at the University of Nebraska-Lincoln, in the US. Together with his team, he has been trying to shed light on this gray area in the food chain for several years. ” It seems obvious that lots of organisms end up with viruses in their mouths all the time, simply because there are very large amounts of them in the water. “, he explains in a press release from the university.

This is all the more surprising since viruses are from a microorganism’s point of view particularly appetizing appetizers. They are composed of nucleic acids, nitrogen and phosphorus – essential building blocks of life as we know it.

Logically, therefore, it is a delicacy that ” everyone should want to eat insists DeLong. ” There are so many things that eat whatever comes their way. So surely something, somewhere has learned to eat these very interesting ingredients. But testing this hypothesis was anything but trivial.

A trace from the plankton

In the absence of concrete conduits, DeLong therefore began by casting a wide net. He collected a large number of different microorganisms from a nearby pond before cultivating them. It still remained to find them a potential meal – a terribly risky process, knowing the diversity of possible interactions between the different species. To maximize his chances of success, he chose to work with cholorovirus.

These are species that parasitize the cells of microscopic green algae. During their life cycle, the infected cells explode. This has the effect of releasing carbon and other nutrients into the medium. And if DeLong chose them, it is because they have already been the focus of another important study of the place of viruses in the food chain.

Chloroviruses attack a chlorophyll algal cell. © University of Nebraska-Lincoln

Traditionally, scientists believed that these elements fed the higher levels of the food chain. But in 2016, biologist James Van Etten showed that most of this material was actually consumed directly by the microbial fauna in a major recycling operation. This has therefore led some researchers, including DeLong, to take a closer look at the virus’ place in this feast for Lilliputians.

He therefore added chlorovirus to his culture before starting an observation phase. The goal: to find an organization, any, that would treat the virus as a snack rather than a threat.

Dumbbellsthe first TRUE viable organism

In time, he made an unexpected discovery from a population, which a population ofDumbbells, a genus of unicellular ciliated microorganisms of the plankton family. These little beasts seemed to be doing surprisingly well. But in microbiology this is a very strong sign; this suggests that the species in question has access to a food source in its immediate environment.

He therefore isolated these little gluttons before serving them another portion. And his perseverance was rewarded. Two days later, the trend had become very clear. The number of chloroviruses has been divided by 100, while the population ofDumbbells was multiplied by 15. In parallel, in another control group without chlorovirus, the bacteria quickly withered away.

Two Halteria seen under a microscope. © Yuuji Tsukii – Hosei University

A very promising result. But before you announce a major discovery, such as the very first organism capable of sustaining itself solely on viruses, it’s better to be sure of your fact. So the team embedded a fluorescent marker into the viruses’ DNA … and the bacteria’s vacuoles—the functional equivalent of the stomach in these organisms—quickly began to glow brightly.

Indisputable proof that a transfer of material did indeed take place between the two populations. And the icing on the cake is that after the fact, DeLong and his colleagues managed to identify several other viable organisms. jackpot !

Major implications in many scientific disciplines

I called my co-authors and yelled, “They pushed! We did it!“”, he recalls in the press release. “It’s exciting to be able to see something so fundamental for the very first time. And that’s not an understatement. In fact, it’s even a greater discovery which could significantly change the way we study food chains.

If we multiply a simple approximation of the number of viruses, the number of ciliates [comme Halteria]and the amount of water on earth, we get a massive movement of energy up the food chain says DeLong. And it goes even further. ” If it happens on the scale that we think, it could completely change our global perception of the carbon cycle. »

The carbon cycle and its four constantly communicating reservoirs. © Wart dark, tooony, bendeck – WikiCommons

As a reminder, the carbon cycle is a phenomenon of gigantic proportions, which describes the life of a carbon molecule and its passage through the various biological, geological, aquatic or atmospheric reservoirs of our planet. It is therefore closely connected with life on Earth at absolutely every level, from the physiology of organisms to the climate of the planet. Suffice it to say that if viruses have a greater than expected influence on this cycle, it will therefore be a very important scientific development.

From now on, the whole challenge will be to document the lives of these viable organisms directly in their natural environments. First, it will determine how they affect the structure of food chains and the evolution and diversity of species. And at this stage, it will eventually be possible to redefine the place of viruses in life on Earth, with all this implies for many other fields of research.

The text of the survey is available here.

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