Mysterious giant viruses have been discovered lurking in the snow and frost of Greenland’s ice sheet. They share the ice with an abundance of algae, meaning this is the first time these viruses – about which we know relatively little – have been found in such a habitat. But that’s not bad news (unless you’re an algae): it’s thought that by infecting microalgae, the giant viruses may act as a sort of secret weapon to keep melting to a minimum.
How gigantic are we really talking about? The viruses cannot be seen with the naked eye, but compared to normal viruses (which are 20-200 nanometers in size) they are relatively large. Giant viruses can grow to 2.5 micrometers (that’s 2,500 nanometers), making them up to 125 times larger than normal viruses, and larger than most bacteria. They also have gigantic genomes, containing about 2.5 million base pairs.
Previously, giant viruses have been found in a variety of environments, including the sea, soil and even in humans. However, this latest discovery marks the very first time they have been found on surface ice and snow teeming with microalgae.
The team behind the discovery believes that they could play an important role here in regulating algal blooms and thus protecting the ice from accelerated melting.
When Arctic algae bloom in the spring, large areas of the ice sheet darken, limiting its ability to reflect sunlight, increasing melting. This is bad news for the environment, which is why the newly discovered giant viruses would be such a boon to ice protection if they can act as a natural algae control, as the researchers suspect.
“We don’t know much about the viruses, but I think they could be useful as a way to reduce ice melt caused by algal blooms,” first author Laura Perini of Aarhus University’s Department of Environmental Sciences said in a statement. “We don’t know yet how specific they are and how efficient it would be. But by investigating them further, we hope to be able to answer some of those questions.”
The team collected samples from various snow and ice habitats in the Greenland Ice Sheet, including dark ice, ice cores, red and green snow and melt holes (cryoconite), before analyzing them for DNA and looking for specific giant virus marker genes. . In almost all samples they found sequences that correspond to known giant viruses.
That’s not dirty water, it’s actually a monster full of microorganisms, including algae and giant viruses.
Image credit: Laura Perini
To make sure these came from active viruses and not long-dead microbes, the researchers also extracted messenger RNA, or mRNA – a single-stranded molecule that contains the instructions from DNA that direct cells to make a protein – from the samples.
“In the total mRNA sequenced from the samples, we found the same markers as in the total DNA, so we know they have been transcribed,” Perini explains. “It means the viruses are alive and active on the ice.”
Your standard viruses are unable to transcribe double-stranded DNA into single-stranded mRNA. Instead, they have free-floating strands of RNA in their cells that are activated when the virus infects its host and uses its machinery. But giant viruses are different. They are able to repair, replicate, transcribe and translate DNA without the help of a host – although we’re not sure why that is.
When it comes to giant viruses, there are plenty of other unknowns. For example, what do these mysterious microbes infect?
“Some of them may infect protists, while others attack the snow algae. We just don’t know for sure yet,” Perini added.
But with further research, she hopes we can better understand these pathogens and their potential role in protecting the ice from accelerated algae melt.
The study has been published in the journal Microbiome.