A virus-only diet can fuel growth in certain microorganisms: study

Researchers say they have successfully observed for the first time the energy-producing potential of a phenomenon known as virovory or the eating of viruses, a process capable of fuelling not only the growth of an organism but also its population.

A team from the University of Nebraska—Lincoln says in a study, published on Dec. 27 in the peer-reviewed journal Proceedings of the National Academy of Sciences, it has shown that for some organisms, viruses can serve as a source of nutrition.

“They’re made up of really good stuff: nucleic acids, a lot of nitrogen and phosphorous. Everything should want to eat them,” John DeLong, an associate professor of biological sciences at Nebraska, said in a news release.

“So many things will eat anything they can get a hold of. Surely something would have learned how to eat these really good raw materials.”

The study is based on the team’s work into Halteria, microscopic ciliates that populate freshwater around the world.

Ciliates are single-celled organisms that have short hairs called cilia, which they use for movement.

Researchers found that Halteria can eat large numbers of chloroviruses, which are known to infect microscopic green algae.

Invading chloroviruses burst open green algae, spilling carbon and other elements into their aquatic habitats, the researchers say, which then is taken up by microorganisms.

By eating these viruses through virovory, the researchers suggest that this energy instead moves up the food chain.

“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),” DeLong said, adding ciliates in a small pond might eat 10 trillion viruses a day.

“If this is happening at the scale that we think it could be, it should completely change our view on global carbon cycling.”

The researchers tested this by collecting samples from a nearby pond, gathering the microorganisms in those samples into drops of water, adding chlorovirus and checking in 24 hours later.

The Halteria grew an average of about 15 times larger over two days and reduced the number of chlorovirus by as much as 100-fold over that same period, the researchers say. Halteria with no chlorovirus, meanwhile, did not grow at all.

“At first, it was just a suggestion that there were more of them,” DeLong said of the ciliates. “But then they were big enough that I could actually grab some with a pipette tip, put them in a clean drop, and be able to count them.”

The researchers confirmed that the Halteria were eating the virus by tagging some chlorovirus DNA with a fluorescent green dye. Later, they found that the vacuole, or stomach, of the Halteria were glowing green.

“I was calling up my co-authors: ‘They grew! We did it!'” DeLong said. “I’m thrilled to be able to see something so fundamental for the first time.”