The University of Nebraska’s John DeLong and colleagues revealed that a type of Halteria—microscopic ciliates found in freshwater settings across the world—can ingest a large number of infectious chloroviruses. For the first time, laboratory studies by researchers have shown that a virus-only diet, or “virovory,” may support an organism’s physiological growth and even population expansion.
These organisms, known as protozoa, were found in the surface waters of the Gulf of Maine and the Mediterranean Sea off the coast of Catalonia, Spain. They found a slew of viral DNA associated with two diverse groups of protozoans, called choanozoans and picozoans; the same DNA sequences cropped up in many members of the two groups, despite some of these single-cell organisms not being closely related.
The initial discovery of chloroviruses, which are known to infect small green algae, was made by James Van Etten of Nebraska University. The invading chloroviruses finally burst their single-celled hosts like balloons, releasing carbon and other life-sustaining elements into the surrounding seas.
According to DeLong, an associate professor of biological sciences at Nebraska, ciliates in a tiny pond might consume 10 trillion viruses daily. “If you multiply a rudimentary estimate of how many viruses there are, how many ciliates there are, and how much water there is, it comes out to this huge quantity of energy transfer (up the food chain),” he said. “If this is happening at the scale we think it could be, it should completely change our view on global carbon cycling,” he added.
This discovery changed DeLong’s perspective on investigating viruses, putting him in “a different headspace.” He reasoned that even putting aside infection, the presence of viruses and bacteria in the water made it unavoidable that the former would occasionally end up inside the latter. “It seemed clear that everyone and everything was constantly ingesting viruses,” he added. Because there is so much of it in the water, it seemed certain that it must be taking place.