A type of freshwater plankton has become the first organism seen to thrive on a diet of viruses, according to a new study by researchers at the University of Nebraska-Lincoln in the US.
Viruses are often consumed incidentally by a wide range of organisms, and can even spice up the diets of certain marine protists. But to qualify as a true step in the food chain, described as a virovorium, viruses must provide a significant amount of energy or nutrients to their consumer.
The Halteria microbe is a common genus of protist known for fluttering as its hair-like cilia propel it through water. Laboratory samples of the ciliate not only consumed the chloroviruses added to their environment, but the giant virus fueled the growth of Halteria and increased its population size.
The spillover effects of widespread consumption of chloroviruses in nature could have a profound impact on the carbon cycle. Known to infect microscopic green algae, chloroviruses cause their hosts to break down, releasing carbon and other nutrients into the environment, a process that could be limiting in large numbers if they feed on viruses.
“If you multiply a rough estimate of how many viruses there are, how many ciliates there are, and how much water there is, you get this huge amount of energy movement up the food chain,” says ecologist John DeLong of the University. from Nebraska-Lincoln.
“If this is happening on the scale that we think it could be, it should completely change our view of the global carbon cycle.”
The research has taken three years to develop and was based on the idea that the large number of viruses and microorganisms that can be found in the water may well cause the former to be eaten by the latter, although there have not been many previous studies. that scientists could refer to as a reference.
There are some good things inside viruses if you are an organism looking to feed, including amino acids, nucleic acids, lipids, nitrogen, and phosphorous. Surely something would want to make a meal out of it, the researchers reasoned.
The team collected pond water samples and spiked them with chlorovirus, looking to see if any species treated the viruses as food rather than a threat. That led them to Halteria and Paramecium, both of which thrived in water.
As the Paramecium fed on the viruses, their sizes and numbers barely budged. Halteria, on the other hand, fed on them, using the chlorovirus as a nutrient source. The ciliate population grew about 15-fold in two days, while the virus population dropped 100-fold.
“At first, it was just a suggestion that there were more than [the Halteria organisms]says DeLong. “But they were big enough that I could grab some with a pipette tip, put them in a clean drop, and count them.”
Green fluorescent dye was used to label the chlorovirus DNA before it was introduced into the two types of plankton. This confirmed that the viruses were eating: the vacuoles, the microbial equivalent of stomachs, glowed green from feeding.
Further analysis revealed that the growth of Halteria compared to the decline of chlorovirus matched the ratios seen in other microscopic predator vs. prey relationships in aquatic environments, giving the team more evidence of what was going on.
There is still much more to explore here. Next, the researchers want to see how virovors might affect the food web, the evolution of species, and the resilience of populations. However, before that, they need to collect evidence that it happens in nature.
“I was motivated to figure out if this was weird or not, or if it fit,” says DeLong. “This is not strange. It’s just that no one noticed it.”
“Now we have to find out if this is true in nature.”
The research has been published in PNAS.
Source: news.google.com