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Go to Brilliant.org/SciShow to learn how you can take your STEM skills to the next level! [♪ 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 mosquitoes 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 mosquitoes 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, mosquitoes 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 mosquitoes. But in a 2009 experiment, scientists took some Wolbachia and managed to infect a group of Aedes aegypti mosquitoes with it. Those are mosquitoes that carry a whole bunch of diseases, including avian malaria.

Then, they had those mosquitoes 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 mosquitoes 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 — and not just for the amphibians.

Because violacein also has antibacterial and even anti-cancer properties. So it might be able to protect us, too. You might not see it when you look at them, but coral really need algae.

The coral provides the algae with a safe place to live, and the algae give the coral all kinds of nutrients it needs to survive. So when that relationship is disrupted, bad things happen. Like coral bleaching.

In the presence of stressors like rising temperature, corals expel their algae, which makes the coral turn white and become vulnerable to disease. Bleaching can also stunt their growth and negatively affect their ability to reproduce. And a severe bleaching event can kill them.

When we filmed this in early 2020, 27% of the world's coral reefs had already been lost due to bleaching, and experts think that number is likely to go up. But maybe it doesn't have to. In 2018, researchers created a cocktail of different microorganisms, each of which possessed certain protective qualities.

Some were chosen for their ability to produce catalase, which can reduce the concentration of dangerous, reactive oxygen species — ones that would damage proteins or genetic material and kill cells. Other microbes were good at converting nitrogen into a nutrient the corals could use, while others were aggressive toward pathogens. And when scientists added these microbes to a coral community, they reduced bleaching in the presence of warmer water and pathogens!

Which is great! That doesn't mean the microbes prevented or reversed bleaching, though — they were just able to help the coral survive the bleaching event with fewer ill effects. It still takes a reduction in water temperature and the return of algae to get the coral back on track.

But maybe something like this could keep corals afloat during short warm spells. Finally, cleaning the messes humans have made remains one of our biggest challenges. And nowhere is this more evident than in superfund sites.

These are some of the most polluted places in the United States, and they get their name, superfund, from the trust Congress established to help pay for their cleanup. Not superfun (it's hard to say it), superfund. And that cleanup is expensive and it's dangerous — for humans and for our non-human helpers.

Poplar trees, for example, can naturally help remove a common industrial solvent called trichloroethylene, or TCE, from heavily-contaminated sites. But in the process, the toxicity may cause them to become stunted:. Their leaves can turn yellow, and their branches can wither.

Some may even die. So, there's a balance here. Because trees are a great way to clean up polluted areas… but we also don't want to kill them.

Cue the microbes! In 2017, researchers discovered that poplar trees fortified with a kind of Enterobacter bacteria were able to remove the TCE with fewer ill effects. This specific strain of Enterobacter — called PDN3 — breaks down the TCE and releases a harmless chloride ion instead.

Researchers inoculated poplar trees by exposing their roots to the bacteria for one week, then checking to make sure that the bacteria was able to colonize the roots. The trees that were inoculated not only removed more TCE from the environment, but they were also healthier and larger than the trees that didn't get any microbial assistance. Because, like, when a toxin isn't trying to wither your leaves and kill you, it turns out you can do your job better.

So, despite our aversion to them, because yes, they can kill you, almost all microbes are either benign or positive. They make your yogurt yogurty and they make your cheese cheesy. But more than that, they can also help or even save species across the planet.

If you want to learn more about microbes, good news:. There is so much to learn about them, from their behavior to their genetics. But if you really want to dive in, it might be good to know a bit about computational biology.

This field combines elements of physics, computer science, and bio. And if you want to get a sense of what it looks like, you can check out. Brilliant's Computational Biology course.

It covers things like genomes, DNA composition, and molecular folding — all things that are important in the lives of microbes. And like all of Brilliant's courses, it does that in a really engaging, easy-to-understand way. So, props to them!

If you want to check it out, you can go to Brilliant.org/SciShow. And the first 200 people to sign up there will get 20% off the annual Premium subscription. [♪ OUTRO].