Viruses are found in astronomical numbers everywhere on Earth, from the atmosphere to the depths of the oceans.

Even its biomass equals about 25 billion people, but the strange thing, despite its abundance and richness in nutrients, is that there are no known living organisms that use it as food.

There is an increasing number of evidence indicating that at least one group of organisms may feed on viruses, namely "protozoans and single-celled microorganisms".

Researchers in Frontiers in Microbiology published on September 24, 2020, the first convincing evidence that two groups of environmentally important primate marine organisms, Choanozoa and picozoa, two virus eaters, hunt prey through a process. Ingestion.

A big surprise

Dr. Ramonas Stepanuskas is the study lead and director of the Single-Cell Genomics Center at the Bigelow Laboratory for Ocean Sciences in Maine.

"Our data show that many protoplast cells contain the DNA genes for a wide range of non-infectious viruses rather than bacteria, which is strong evidence that they feed on viruses rather than bacteria. This came as a great surprise," Stepanoskas says.

He adds that these results conflict with prevailing views on the role of viruses and protozoans in marine food webs.

If the results of the study are correct, then a centuries-old doctrine will be turned upside down, instead of considering viruses only pathogens to considering that they play a role in fueling and preserving life.

"Viruses are rich in phosphorous and nitrogen, and can be a good supplement to a diet rich in carbon," says Julia Brown, a microbiologist at Bigelow's lab and first author of the study, in the press release published on the Eurek Alert scientific site.

Also, "removing viruses from the water may reduce the number of viruses available to infect other organisms."

Two groups of protozoan marine creatures, Choanozoa and picozoa, are virus eaters that they catch by ingestion (Malticil Genome Lab - Wikipedia)

Sample collection and analysis

Ramonas Stepanuskas and colleagues started this research project more than a decade ago.

Initially, they intended to study the marine pioneer preference for prey, many of which feed on bacteria, but the results surprised them.

Surface seawater samples were taken, including 1,698 pioneer individuals, from the northwestern Atlantic Ocean in the Gulf of Maine, USA in 2009, and the Mediterranean Sea off Catalonia, Spain, in 2016.

Stepanoscas and colleagues then divided the cells and analyzed their contents.

The team concluded that any genetic material that differs from the genetic material of the protists may be a sign of something they ate.

After repeated rounds of analysis, the researchers were surprised to find that there wasn't much bacterial material expected to be found.

Instead, there were viruses of all shapes and sizes.

Even viral genes have been found in the cells of all precursors of the reptile and picosa groups.

It was a strange discovery, says Julia Brown.

Although since the 1990s researchers have assumed that some early species may be able to use viruses as food, this research has not received much attention after that.

A sample of 1,698 pioneer individuals, taken from the Gulf of Maine and the Mediterranean (Ramonas Stepanoscas et al. - Eurek Allert)

The issue of viral consumption

However, finding viral genetic material in or around a cell does not guarantee that the virus was once food.

For example, some viruses may have infected the protists or are simply stuck to cell surfaces.

However, Dr. Brown says it is "very unlikely that these viruses are capable of infecting all the protists in which they are found."

"The new study alone cannot prove the consumer relationship between protists and viruses," says Rika Anderson, a microbial ecologist at Carleton College in Minnesota who was not involved in the study, in a report published in the New York Times.

The researchers divided the precursor cells and analyzed their contents, and there were viruses of all shapes and sizes (Ramonas Stepanoscas et al. - Uric Allert)

But protists are found in a mind-boggling array of habitats, such as rotting tree stumps and animal guts, and they may have at least developed several strategies to feed themselves. ”“ They kind of eat everything, I wouldn't be surprised if they were feeding on viruses. ”

Dr. Stepanowskas and Dr. Brown say that some types of viruses are only found in certain groups of protists, hinting that this was not a mere coincidence.

And if it does turn out that viruses are the food of the protists, it remains unclear whether they depend on them as part of a varied diet or if they exclusively feed on them.