Lurking in the snow and frost of the Greenland ice sheet, mysterious giant viruses have been discovered. 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 a habitat. But it’s not all bad news (unless you’re an algae): it’s thought that by infecting the microalgae, the giant viruses could act as some sort of secret weapon to minimize melting.
What giant are we talking about? Viruses cannot be seen with the naked eye, but compared to your average viruses (which are 20-200 nanometers in size) they are relatively massive. Giant viruses can grow up 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 huge genomes containing 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 first time they have been found on the surface of ice and snow teeming with microalgae.
The team behind the discovery believes that here they could play an important role in regulating algal blooms and therefore in protecting the ice from accelerated melting.
When arctic algae bloom in the spring, they darken large areas of the ice sheet, limiting 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 protection if they can act as natural algae controls, as the researchers suspect.
“We don’t know much about viruses, but I think they could be useful as a way to alleviate ice melting 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. But by exploring them further, we hope to answer some of these 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 matching known giant viruses.
It’s not dirty water, it’s actually a sample full of 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 the instructions from DNA that direct cells to make 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 are transcribed,” explained Perini. “That means the viruses live and are active on the ice.”
Your standard viruses are not capable of transcribing 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.
When it comes to giant viruses, there are many other unknowns. What do these mysterious microbes infect, for example?
“Some of them may infect protists, while others attack snow algae. We just can’t be 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 algae-accelerated melting.
The research is published in the journal Microbiome.
