Thursday, September 24, 2015

Ice, Ice Baby: Bringing Frozen Viruses Back To “Life”

Back in 2003, a new class of giant, ancient viruses were found that preyed upon unsuspecting amoebas in the Paleolithic.  

Earlier this year, scientists published a study describing how they revived another one of these giant viruses, which has been frozen in Siberian permafrost for 30,000 years! We’ll discuss why they did this in a bit, but let’s first talk about how they did this.

Over the years, lots of cool stuff has been found well-preserved in ice. Otzi, a 5,000 year old “ice man” was a historic find in 1991. He went on to become a spokesperson for the GEICO auto insurance company.
Viruses are minute obligate intracellular parasites. In other words, they cannot replicate outside of a host cell, an attribute that gives them the unflattering distinction of being the worst houseguest ever. That’s right:  viruses storm into your home – unannounced – take off their coat and make themselves right at home. They ransack the place and raid your fridge without even asking. As if that wasn’t bad enough, you come home one day and catch the virus in the act of making babies – lots and lots of babies. Finally, this unruly family blows up your house as they leave, without so much as a “thank you”, and go on their merry way to invade other homes in your neighborhood.

While we can feel the pain that they cause, especially during cold and flu season, we can’t see the culprits. Viruses are really, really tiny - most are smaller than the molecular complex cells use to make proteins.
Many viruses are under 100 nM (0.1 micron), but some (like Ebola) are almost 1.0 micron. Compared to viruses, even a bacterium is enormous. 
So how does one find a virus in thousands of miles of ice? Virus hunters take an approach similar to finding a needle in a haystack. But in this case, instead of a magnet, the scientists use amoebas as “bait” to lure out viruses that might be chilling out in the permafrost.

Amoebas are single-celled organisms called protozoa that, like most cells, fall prey to viruses. By putting permafrost into amoeba cultures, scientists were able to screen samples for those that could kill the amoebas. And they found a “big” surprise.

Thick membrane or no, Pithovirus invades amoebas. Who knows…with this discovery, maybe scientists can devise a new treatment that targets the deadly brain-eating amoeba, Naegleria.
The virus spotted in these infected amoeba cultures resembled a so-called “pandoravirus” or “giant” virus. They are still microscopic of course, but considerably larger than the viruses we know of today (about 1.5 microns in length and 0.5 microns across). Not only are they larger in size, but they contain many more genes. By way of comparison, HIV contains less than 15 genes, but this giant virus has 500 genes. They christened this new giant virus “Pithovirus sibericum”, and it is the oldest virus ever to have been revived to date.

A “huge” find in the world of virology, Pithovirus is now growing in labs again after a 30,000 year slumber. Image taken from Legendre, et al.
Now why on earth would scientists bring a virus back from the dead? Are they mad? Are they trying to facilitate the apocalypse?

Of course not. As climate change continues to melt more and more ice, it is possible that these viruses are going to revive naturally. By resurrecting them in the lab in controlled conditions, researchers can get ahead of this curve by studying the virus. Study of the virus can help determine which one(s) pose a threat and, if so, vaccine and drug development efforts can get underway thanks to our knowledge of the virus. And don’t worry about Pithovirus – it was already found to be incapable of infecting animal cells.

Another reason these viruses are worthy of study is that they can reveal new insights into how cells evolved, since viruses can transfer their DNA to their hosts. They may even shed light on the greatest biological mystery:  the origin of DNA/RNA and how life came to be on Earth.

The same team of scientists isolated yet another ancient giant virus this year from the same permafrost and named it Mollivirus sibericum. You may also be wondering what Siberian virus hunters listen to while exploring those Hoth-like landscapes. I'll take a guess and hope that it is wrong...

Contributed by:  Bill Sullivan, Ph.D.
Follow Bill on Twitter.

Legendre, M., Lartigue, A., Bertaux, L., Jeudy, S., Bartoli, J., Lescot, M., Alempic, J., Ramus, C., Bruley, C., Labadie, K., Shmakova, L., Rivkina, E., Couté, Y., Abergel, C., & Claverie, J. (2015). In-depth study of , a new 30,000-y-old giant virus infecting Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1510795112
Legendre, M., Bartoli, J., Shmakova, L., Jeudy, S., Labadie, K., Adrait, A., Lescot, M., Poirot, O., Bertaux, L., Bruley, C., Coute, Y., Rivkina, E., Abergel, C., & Claverie, J. (2014). Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology Proceedings of the National Academy of Sciences, 111 (11), 4274-4279 DOI: 10.1073/pnas.1320670111

No comments:

Post a Comment