it is for us to know what viruses may be lurking out there.

But while we keep one wary eye out for those potentially harmful ones, we're also uncovering

just how much viruses have actually shaped humans—and the rest of life on Earth—in

some really surprising ways.

'Virus hunters', as they're known, are

scientists who search the hidden corners of the world for viruses that are poised to become

human pathogens. In many cases, they're searching for Disease

X. That's not the name of an actual illness—it's what we call the hypothetical infection that

could cause the next big global disease. The idea is to find it before it finds us.

But other researchers are delving into what else viruses are doing on our planet besides

making people sick. It's estimated that there are about this many individual viruses

on our planet.

And we've only made the most miniscule dent

in that number: we've found and classified about 9,000 of the viruses on Earth.

And of those, only about 200 are known to cause disease in humans.

But over the past decade, scientists have been identifying new viruses by the thousands.

And the main tool they're using to do that...is metagenomics.

This is actually something I'm using in my own research on bacterial communities,

so let's break it down together.!

In metagenomic sequencing, we take a sample—that

can be soil, ocean water, a bodily fluid—and we purify it down to the genetic material

of just the stuff we're looking for. In this case, let's say it's viruses.

So now we have the genomes of all the viruses in our sample. Lets picture each virus's genome

as a piece of paper with sentences on it.

Because the next step—and this sounds nuts— is that we rip each

piece of paper up into little strips with just sentences on them.

We do this because our sequencing

machine has to 'read' all of these genomes.

And, if you can picture, it's much faster for lots of people to each read a sentence.

And they can each read their sentence at the same time a sentence

than it is for one person to read a whole page, one at a time.

That's what we're doing

when we divide our genome up into little chunks. Now that we've read the sentences in a super

efficient way, we can put the sentences back together into the full page, or the full genome.

Then we compare that to a library full of known genomes.

So we can say, 'this unknown page is the same as this known page that we have on file'.

It's a match! We've ID'ed the virus in our sample.

And we do this for every virus in our sample.

Metagenomic sequencing is an

incredibly useful tool that lets us identify huge numbers of microbes really fast.

And as scientists have turned that powerful lens on our world to catalogue viruses...they've

been astonished at just how many they're finding, everywhere. In the ocean, in our

wastewater, inside the spiders in our gardens and of course, inside us. Most of them are

totally harmless to humans, and many of them are totally new to science!

The viruses in the ocean? They're preying on other marine microorganisms, releasing

nutrients. This may be the bottommost foundation of the ocean's food web.

The viruses in every ecosystem? They help maintain our planet's biodiversity by keeping

other species in check. If viruses suddenly vanished from the planet, it's likely that

the balance of other organisms would rapidly get out of whack.

And one other major result of all this sequencing is a new understanding of just how thoroughly

viruses have shaped life on Earth as we know it.

Because they invade living cells to replicate, they're equipped to take over a host's

genetic replication machinery—sometimes, viral genetic material gets incorporated into

the host's. It's estimated that around 8% of human DNA actually came from a virus,

including some of our most important skills. Like, the ability of modern humans to give

birth probably came from a piece of viral genetic code that jumped over to its mammalian

host about 130 million years ago. That gave us our ability to grow a placenta. So, yep.

We got hacked, and it's probably the reason we don't lay eggs.

Scientists don't know how many more viruses are out there, waiting to be discovered. And

of those, we have no idea how many of them may be harmful to us.

But sequencing at least some of those nonillion viruses out there is the first step. The next

step is to identify what they're living inside...and how exactly these tiny, invisible

puppeteers are pulling the strings of our natural world.

If you want more on just how many viruses are in our oceans and what they're doing

there, you can check out this video, and leave us a comment down below if there's another

viral topic you'd like to see us cover. Keep coming back to Seeker for all your microbial

updates and as always, thanks for watching. I'll see ya next time.