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[♪ INTRO]

Ever since humans found out germs were a thing,

we've had a vendetta against microbes.

The idea that death can be doled out by stuff we can't even see

is pretty unsettling.

So we invented antibacterial soap and antibiotics and antifungals,

and we went a little bit overboard in the end with the anti-everythings.

And as a result, we've often ignored the existence of good microbes.

With the exception of the ones that give us cheese and yogurt

and beer and bread, of course.

We've always given them a free pass.

But good microbes do a lot more than make yogurt yogurty

and cheese cheesy.

They also help us digest food and fight illness.

And the more we've learned about them, the more we've realized

that they have the capacity to do really big things.

Like help us protect endangered species and maybe even undo

some of the big mistakes we have made as humans.

So here are six examples of microbes helping to save the world.

The first, koalas. They are notoriously picky eaters.

Although they've occasionally been seen eating leaves

from other trees, for the most part, they eat eucalyptus leaves.

And that's pretty much it.

And they're even picky about which species of eucalyptus they eat.

So, these things are cute, but they're also, like,

the worst dinner guests of all time.

Thankfully, that's not too much of an issue for them.

Australia is full of eucalyptus trees, and there isn't a lot of competition

for it since the plant's leaves are toxic.

Koalas can only digest it thanks to a special type of gut bacteria —

one they acquire as babies when they eat what's called pap.

That's a special kind of microbe-rich poop

that they get from their moms.

So overall, this lifestyle works for them. Or it did.

In the next sixty years, climate change is expected to

reduce the distribution of most Australian eucalyptus species

by more than half.

Urbanization and habitat destruction are also a threat,

and that was before the devastating Australian wildfires

(which started in 2019) added even more pressure.

In response to this, you would think koalas might switch

to another food source.

But they don't always do that — in part, because

their digestive systems are just so specialized

to one or a few species of eucalyptus.

Fortunately, there's a pap for that.

In 2019, scientists successfully transplanted the gut bacteria

from koalas who ate one type of eucalyptus, called messmate,

into the guts of those who were used to eating another type,

called manna gum.

Specifically, they gave the manna gum koalas capsules

that contained microbes extracted from the poop of messmate koalas.

Which is like, you know, slightly less gross than eating actual poop.

The scientists hoped that the unique microbes from the messmate koalas

would help the other group's bodies digest the new food.

And at the end of the experiment, the manna gum eaters

were eating more messmate. So… success!

To be fair, though, the researchers weren't totally sure

if this happened because of the increase in gut bacteria,

or if the gut bacteria were increasing because the koalas were eating

more messmate for some other reason.

So there's room here for more research.

But it's intriguing to think that poop and the bacteria it contains

might one day help save a species.

To the delight of poop joke enthusiasts everywhere.

Next, malaria is one of humanity's most deadly foes.

But we aren't the only species that gets it.

Bats, reptiles, birds — there are a lot of animals on malaria's hit list,

although not all of them are affected by it the way we are.

Take avian malaria, for example.

Although it can shorten birds' lives, it usually doesn't kill them.

In some isolated places, though, avian malaria can be deadly. Like in Hawai'i.

Until humans came along, birds in Hawai'i had no exposure

to the malaria parasite — because there were no mosquitos

on the Hawaiian Islands.

According to a local legend, that only happened when a bunch of sailors

dumped a barrel full of water and mosquito larvae

into the wetlands around Lahaina.

Which… did that seem like a good idea?

When the mosquitos arrived, so did the avian malaria parasite.

And after native Hawaiian birds were introduced to it,

ten species went extinct.

Thankfully, there might be a way to control this disease in Hawai'i

and all over the world.

And it's not insecticide — because although that's been the standard for years,

mosquitos have an annoying habit of becoming resistant to it.

Instead, scientists are testing a new weapon: a bacteria called Wolbachia,

which naturally infects a lot of other insects,

but not malaria-carrying mosquitos.

But in a 2009 experiment, scientists took some Wolbachia

and managed to infect a group of Aedes aegypti mosquitoes with it.

Those are mosquitos that carry a whole bunch of diseases,

including avian malaria.

Then, they had those mosquitos drink the blood of chickens

infected with the avian malaria parasite.

And normally, this would result in the insects becoming malaria carriers.

But in this case, the mosquitos actually appeared to have

a stronger immune response, and fewer malaria parasites developed.

Right now, scientists aren't completely sure why this works,

but it could be because the mosquito's immune system

gets a boost in the presence of Wolbachia.

And as a bonus, this method also works to prevent other diseases,

including mosquito-borne human ones like dengue and Zika,

which are also carried by A. aegypti.

If you've ever tried to enjoy a day at one of the Midwest's Great Lakes,

you may have noticed a bunch of tiny, pokey shells all over the beach.

Those are invasive zebra mussels, and they're there just to ruin your afternoon.

Or so it seems like, anyway.

In reality, invasive mussels are a huge problem

not just because it hurts to step on them,

but because they are extremely difficult to control.

Juveniles are microscopic and will attach themselves to almost any hard surface,

which means boat owners can accidentally transport them from one lake to another.

And when they do, these mussels clog the intake pipes

that feed city water supplies, they hog nutrients, and they steal food

from native fish and other aquatic species.

In the US, they cost the economy around a billion dollars every year.

Fortunately, scientists have figured out how to use

the mussels' own diet against them.

See, mussels usually eat plankton,

but they also eat bacteria.

And after testing more than 700 strains, researchers learned that a common,

usually harmless bacteria called P. fluorescens produces a toxin

that's dangerous to the mussel's digestive system.

It causes cells to rupture and die in the mussels' digestive gland,

and that ultimately kills the animal.

Maybe more importantly, though, when mussels feed on this bacteria,

they don't notice anything's wrong; they seem to think they're having

just a nice and lovely day.

And they will keep eating until they die.

This is huge, because although chemicals like chlorine

are a more obvious threat to the animals, mussels can sense

those chemicals and will shut their valves to protect themselves.

The bacteria, meanwhile, just masquerades as normal food.

Scientists have been looking into this biological solution

to the invasive mussel crisis for decades, but in the last few years,

that research has finally started translating into practical use.

So someday, we might be thanking P. fluorescens for our clean,

mussel-free beaches.

A common forest salamander has a weird way of weaving

in and out of its clutch of eggs.

And it's not just being mysterious: It's transferring an antifungal bacteria

from its skin onto its eggs.

The bacteria helps protect the eggs from a common type of fungus.

But when scientists saw this, they wondered if there might be

another application for that antifungal.

They wanted to know if it could also be used to prevent a deadly

chytrid fungus, which infects more than 500 amphibian species

around the world.

Biologists have tried a number of strategies to control this fungus,

but none of them seem practical for large populations,

and others have had nasty side effects.

So hey, maybe this salamander stuff could be the solution.

In 2009, researchers tested their hypothesis on mountain yellow-legged frogs,

which are very susceptible to chytrid.

It attacks tadpoles' mouths and damages adults' skin,

so infected frogs typically die.

In their experiment, scientists bathed frogs in a bacterial soup

made from J. lividum, the same bacteria found on the skin

of those salamanders.

And when those frogs were exposed to the fungus, none of them died.

Meanwhile, frogs who didn't get a bacterial bath weren't so lucky.

Over 80 percent of them didn't survive the fungus.

This treatment seems to work because the bacteria produces an antifungal

called metabolite violacein, which inhibits the fungus somehow.

Scientists have tried to figure out how this works, but they're not sure.

They think it might be a byproduct of violacein's interactions

with other bacteria.

In any case, it works, so they're going to keep doing it —