An organism that feeds only on viruses has been discovered for the first time

(ORDO NEWS) — A viral particle that has penetrated a cell often means trouble for the host, but the tiny ciliate has turned this rule inside out. For her, viruses are not a danger, but food.

Halteria ( Halteria ) are found in fresh waters around the world – tiny ciliates that are distant relatives of the ciliate shoe known to us.

True, if their famous relative mainly feeds on bacteria, fungi and algae, then Halteria’s favorite dish is chloroviruses.

They infect microscopic green algae, which ultimately leads to the death of the hosts: their cells burst from the inside, like a bursting balloon, and the viral particles go out.

But even in the microcosm, no one can be exclusively an “eater”: each drop of water contains tens of millions of viruses, so that, according to John DeLong ( John DeLong ), in one single day in a small pond, halteria can digest up to 10 trillion chloroviruses.

Previously, scientists have already recorded the very fact of eating viruses by single-celled microorganisms, but never before have they found a microbe that would make viral particles its main source of nutrition.

Viruses were traditionally thought to be too low in calories to provide energy for even the smallest predator.

Nevertheless, their particles contain proteins, fats and nucleic acids, which makes them quite an attractive food object.

And indeed: even on a diet consisting of only viruses (for this we had to come up with a new term – “viro-eating” ( virovory ), by analogy, for example, with carnivory ( carnivory ), halteria successfully grow and multiply.

In just a day of incubation in a drop of water, to which the researchers added a generous portion of chloroviruses (there were no other food sources there), the number of halteria increased 15 times.

In the meantime, the number of viruses has decreased by a factor of 100, which is quite consistent with the predator-prey relationship from any other ecosystem.

Although the number of halteria did not increase in drops without chloroviruses, a team of researchers from the University of Nebraska at Lincoln (USA) decided to finally clarify whether halteria eat viruses.

To do this, they labeled the DNA of the chlorovirus with a fluorescent green dye – and soon the halteria, which were offered the “labeled” viruses, also began to glow green.

An organism that feeds only on viruses has been discovered for the first time 2
The dynamics of the number of halteria (A) and chloroviruses (B) fully corresponds to the pattern of relations between predator and prey

The results of the study are interesting not only because this is the first known case of virophagy in living organisms.

They also force us to reconsider the entire carbon cycle in the microcosm, where viruses not only contribute to its release from infected cells, but can themselves serve as its source for voracious virovorous ciliates.

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