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Some pond organisms feed solely on viruses

A team of researchers led by the University of Nebraska–Lincoln has found that over the course of one day, in the placid waters of a single pond, a million virus particles might enter a single-celled organism known for its minuscule hairs (called “cilia”) that helps it propel through the water. According to the experts, those virus particles are far from being just a source of infection: they may in fact be a crucial part of the nutrition of these microscopic ciliates.

By collecting and analyzing samples of water from a pond in Nebraska, the scientists discovered that a species of Halteria – a microscopic ciliate populating freshwater worldwide – can eat enormous numbers of infectious chloroviruses which share their aquatic habitats. Thus, a virus-only diet – dubbed by the researchers “virovory” – is often enough to fuel the physiological and even population growth of an organism.

Chloroviruses have long been known to infect microscopic green algae, bursting them like balloons and spilling carbon and other life-sustaining elements into the open water. That carbon, instead of going to the predators of these tiny creatures, gets vacuumed up by other microorganism, in a rather grim – and perpetual – recycling program.

“That’s really just keeping carbon down in this sort of microbial soup layer, keeping grazers from taking energy up the food chain,” said study lead author John DeLong, an associate professor of Biological Sciences at Nebraska.

However, if ciliates eat those same viruses, then virovory could be counterbalancing the carbon recycling which the viruses are known to perpetuate. Thus, virovory may be aiding and abetting carbon’s escape from the dregs of the food web, granting it an upward mobility that viruses otherwise suppress.

“If you multiply a crude estimate of how many viruses there are, how many ciliates there are and how much water there is, it comes out to this massive amount of energy movement (up the food chain). If this is happening at the scale that we think it could be, it should completely change our view on global carbon cycling,” DeLong explained.

Further research is needed to clarify how this fascinating process shapes the structure of aquatic food webs, which other species are involved in similar activities, and how virovory may help some species of microorganisms escape extinction.

The study is published in the journal Proceedings of the National Academy of Sciences.

By Andrei Ionescu, Staff Writer

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