Mysterious giant viruses have been discovered in the snow and frost of the Greenland ice sheet. They share the ice with an abundance of algae, meaning it’s the first time these viruses – about which we know relatively little – have been found in such an environment. But it’s not all bad news (unless you’re algae): it’s thought that by infecting microalgae, giant viruses can act as some kind of secret weapon in minimizing melting.
How giant are we talking? Viruses are not visible to the naked eye, but next to your regular viruses (which measure 20-200 nanometers), they are quite massive. Giant viruses can grow up to 2.5 micrometers—that’s 2,500 nanometers—making them up to 125 times the size of normal viruses and larger than most bacteria. They also have huge genomes that contain about 2.5 million base pairs.
Giant viruses have previously been found to persist in all kinds of environments, including the sea, soil and even humans. However, this latest discovery marks the very first time they have been found on the surface of ice and snow teeming with microalgae.
Here, the team behind the discovery believe they could play an important role in regulating algal blooms and subsequently protecting the ice from accelerated melting.
When arctic algae thrive in the spring, they darken large swathes of the ice sheet, reducing its ability to reflect sunlight, which in turn increases melting. That’s bad news for the environment, which is why the newly discovered giant viruses would be such a boon to ice conservation if they can act as a natural algae control, as scientists hypothesize.
“We don’t know much about viruses, but I think they could be useful as a way to mitigate ice melt caused by algal blooms,” first author Laura Perini of the Department of Environmental Sciences at Aarhus University said in a statement. “How specific they are and how effective it would be, we don’t know yet. We hope to answer some of these questions as we explore them further.”
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 (cryoconites), before analyzing them for DNA and looking for specific genes for giant virus markers. . They found sequences corresponding to known giant viruses in almost all samples.
This isn’t dirty water, it’s actually a sample teeming with microorganisms, including algae and giant viruses.
Image credit: Laura Perini
To make sure they came from active viruses and not long-dead microbes, the researchers also extracted messenger RNA, or mRNA – a single-stranded molecule that contains instructions from DNA that direct cells to make a protein – from the samples.
“We found the same markers in the total mRNA sequenced from the samples as in the total DNA, so we know they were transcribed,” explained Perini. “That means the viruses live and are 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 exploits its mechanisms. 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.
When it comes to giant viruses, there are plenty of other unknowns. For example, what do these mysterious microbes infect?
“Some of them can infect protists, while others attack snow algae.” We simply cannot be sure yet,” added Perini.
But with more research, he hopes, we can better understand these pathogens and their potential role in protecting the ice from algae-accelerated melting.
The study is published in the journal Microbiome.