A million virus particles can enter a single-celled organisms in the placid waters of a pond.
Over the last three years, the University of Nebraska–Lincoln's John DeLong has been busy discovering a potential tide-turning secret.
A species of ciliates called Halteria can eat a lot of infectious chloroviruses. The team's lab experiments have shown for the first time that a virus-only diet is sufficient to fuel the growth of an organisms.
James Van Etten discovered chloroviruses, which are known to cause diseases. The chloroviruses burst their single-celled hosts, spilling carbon and other life-sustaining elements into the open water. There is a grim recycling program in miniature and, seemingly, in perpetuity, in which carbon is vacuumed up by other microorganisms.
"That's keeping carbon down in this sort of soup layer, keeping grazers from taking energy up the food chain," said De Long, associate professor of biological sciences.
If ciliates are having the same viruses for dinner, it might be counterbalancing the carbon recycling that the viruses do. It's possible that carbon's escape from the dregs of the food chain is aided and abetted by virovory, according to De Long.
"If you take a crude estimate of how many viruses there are, how many ciliates there are, and how much water there is, you get a huge amount of energy movement up the food chain," said De Long. It should change our view on global carbon cycling if this is happening at the scale that we think it is.
Nobody saw it.
De Long knew how chloroviruses can get into a food web. The ecologist collaborated with Van Etten and Dunigan to show that chloroviruses can get access to Paramecia only when tiny crustaceans eat it.
It put De Long in a different place when it came to thinking about and studying Viruses. He figured that even though the water was free of infections, they would still get into it.
He said that it seemed obvious that everything had to be carrying a Viruses in their mouths all the time. There's so much in the water that it seemed like it had to be happening.
De Long wanted to include studies on aquatic organisms eating Viruses and what happened when they did. He left with a small amount of something. A study from the 1980s claimed that single-celled protists could consume viruses. A number of papers from Switzerland showed that protists were removing Viruses from Wastewater.
DeLong said that it was all done.
There was no mention of the consequences to the organisms or the food webs. De Long knew that viruses were built on carbon and other elements. Anything but junk food was what they were.
He said that they are made up of a lot of Nitrogen and Phosphorous. They should be eaten by everyone.
Anything they can get a hold of will eat it. It would have been great to learn how to eat these raw materials.
As an ecologist who uses math to describe predator-prey dynamics, De Long wasn't sure how to investigate his hypothesis. He kept it simple. He would need some people to help. He went to the pond to collect samples. He corralled all of the organisms he could manage into drops of water. He added a lot of chloro virus.
After a day or two, DeLong would look for a sign that any species was enjoying the company of the chloroviruses. He discovered it in Halteria.
It was suggested that there were more of them. They were large enough that I could grab some with a pipette tip and count them.
The number of chloroviruses plummeted in just a couple of days. The population of Halteria was growing at an average rate of 15 times larger over that time period. It wasn't growing without the chloroviruses.
The team tagged some of the chloroviruses with a green dye in order to confirm that the Halteria was consuming it. The vacuole of the ciliate was soon glowing green.
The ciliates were consuming something. The virus was keeping them going.
I called my co-authors to say that they had grown. We did it, we did it. The findings are detailed in the journal. I'm excited to see something for the first time.
De Long was not done. The mathematical side of him wondered if this particular predator-prey dynamic could be similar to the ones he was used to.
The decline of the chloroviruses against the growth of the Halteria was the first thing he showed. Those ecologists have observed that relationship with other hunters. When Paramecia eatbacteria and millimeter-long crustaceans eatalgae, about 18% of the chloroviruses mass is converted into new mass of its own. The rate at which ciliates preyed on the virus matches up with other aquatic case studies.
I was motivated to find out whether or not this was weird or not. This isn't strange. Nobody noticed it.
There are other ciliates that can thrive by eating on Viruses alone. The more they discover, the more likely it is that it is happening outside. How might it affect the structure of the food web? What is the evolution and diversity of species like? They are resilient in the face of extinctions.
He kept it simple again. DeLong will return to the pond once Nebraska's winter ends.
We have to find out if this is true in nature.
The consumption of viruses returns energy to the food chain. The DOI is 10.1073/pnas.2215000 120.
Journal information: Proceedings of the National Academy of Sciences
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