This episode is supported by NordVPN. Right now, NordVPN is offering SciShow viewers
a chance to set up your own Virtual Private Network and start protecting your internet
experience today with 77% off a 3-year plan. Use the code “SCISHOW” at NordVPN.com/SCISHOW. [♪INTRO] Viruses make so many people sick and miserable
that it seems like turnabout—it’s only fair play! Make the viruses get sick for once! But that’s ridiculous… right? Well, maybe not. Virus-infecting viruses, or virophages, are
totally real, because evolution just doesn’t know when to quit. The first virophage, named Sputnik, was discovered
in 2008 by a team of French researchers in a Parisian water tower. But they didn’t discover it alone. Pretty much everything we learn about these
extremely small viruses is linked to the extremely big viruses they infect, called giant viruses. And since giant viruses, like mimiviruses
and pandoraviruses, were only discovered in 2003, this whole field is brand new territory. Giant viruses were discovered infecting amoebas,
and have been found all over the world. It’s not entirely clear whether they can
make humans sick or not. They’ve been isolated within humans a few
times, including people sick with pneumonia, but it’s not 100% clear if they were causing
the illness or just hanging out. And they’re huge… relatively speaking. In terms of their size and genetic complexity,
giant viruses are more like bacteria than most other viruses. Like, mimiviruses are about 500 to 800 nanometers
across and have genomes of around 12 million base pairs. And pandoraviruses are even bigger. Now, mimiviruses are preyed upon by the Sputnik
virophage, which is only 50 nanometers across and has a genome of about 18,000 base pairs. That’s actually not super small for a virus. The bacteria-infecting virus lambda forms
particles of a similar size, and the flu virus actually has a smaller genome. But what’s weird is that even though giant
viruses are big, it doesn’t seem like they should be able to support invaders. Especially since virophages are still…viruses. They’re made of DNA and protein, but they
lack all the cellular replication tools needed to copy DNA, and the translation tools needed
to make proteins. That’s why viruses need hosts. They enter host cells and take over cellular
equipment to make little virus factories. Without a host cell, viruses would never reproduce. And, in this case, the hosts are...also viruses. Mimiviruses can’t copy DNA and protein on
their own either, and have to infect an amoeba to reproduce. That’s where the virophage sneaks in. It infects the mimivirus while it’s infecting
the amoeba and borrows the giant virus factory. So instead of making more giant viruses, the
amoeba churns out the virophage copies instead. This directly harms the giant virus and its
efforts to reproduce, which is what leads researchers to say that virophages are parasites
of giant viruses, not of amoebas. Now, giant viruses are kind of special because
they seem to have some of that cellular equipment, like a few genes involved in protein translation. But they don’t have ribosomes, the big factories
that actually string proteins together. So they can’t get the job done all by themselves. That’s why many biologists exclude viruses
from the tree of life that includes bacteria, archaea, and eukaryotes. If viruses can’t replicate on their own,
they’re not really alive. Scientists can compare various genes to determine
evolutionary relationships, but if you want to go back to the very beginning, you have
to compare something that all cellular life has. That’s ribosomes. Scientists line up the gene sequences of ribosomes
to determine who’s most closely related to whom. Since viruses don’t have ribosomes, that
means there’s no way to fit them into that paradigm. Viruses have historically just not been considered
enough to count as life. Not enough complexity, not a big enough genome
to fit in the same camp as life as we know it. But there’s still a debate going on. Like, maybe we’re being cell chauvinists. After all, viruses don’t have ribosomes,
but we cellular organisms don’t have capsid proteins, which form the coats of many viruses. And giant viruses are supercharging that debate
because they are more complex and they do have big genomes. Not to mention, they have some of that protein-making
machinery that was thought to be unique to us proper protein-making cellular creatures. And the discovery of virophages has fired
things up, too. Virophage DNA can become integrated into the
DNA of its host virus, just like other viral genomes can integrate into cellular hosts. So if giant viruses can be preyed on like
cells... maybe that’s an argument that we should think of them as being more alive. At least, according to some scientists. We’ve only discovered 18 types of virophages
so far, in places as diverse as lakes in Antarctica to contact lens fluid in France. Many of those are just hits in genome searches,
meaning sequences similar to known virophages have turned up in genomic studies. Nothing about them has actually been studied
in detail yet, so we don’t know what they look like or what they infect. Which only sort of counts as discovering them. But it seems like there could be plenty more
of them out there, and virophages and giant viruses might be more common than we expect. The question of whether viruses are alive
isn’t something we’re going to answer in a 4 minute video… because it’s not
something that biologists are going to settle any time soon. The more we try to categorize evolution in
neat boxes, the more curveballs it throws us. It’s a virus-eat-virus world out there. Thanks to NordVPN for sponsoring this episode. I love the internet and I spend a lot of time
on it. But, as much as I love it, the internet is
not always as secure as I would like it to be. With NordVPN, you can make your connection
to the internet safer. Everything you send over a private, password-protected
internet connection is encrypted, which keeps it safe from snoopers. But say you’re watching a SciShow video
in a coffee shop—so, on a public unsecured network—that’s great! May I recommend this episode on caffeine? The thing is, anyone can see what you’re
doing on a public network. This is why websites that involve sensitive
information, like your bank, have H-T-T-P-S in the URL which means everything you do on
that site is encrypted. But even sites that use https can be vulnerable
to more sophisticated attacks. With a VPN (or Virtual Private Network) all
of your data gets encrypted before it ever leaves your computer, then re-routed through
a trusted server before it’s sent onto the site. In the other direction, data sent to you by
the other side is encrypted by the server before it gets to you. So your personal information is totally safe
sounds complicated, but NordVPN does it all for you with over 4400 super fast servers
in 62 countries, and they’re adding new secure servers all the time. And whether you check your private information
on your Android phone, or iPad, or your ChromeBook, NordVPN will work across different operating
systems and one plan can be used on up to 6 devices. Use the code “SCISHOW” and sign up at
NordVPN.com/SciShow to get 77% off a 3-year VPN plan. [♪OUTRO]
