In December 2024, a report came out about a potential  upcoming global catastrophe.

Thirty-eight scientists had  teamed up to issue a warning. They predicted just how devastating  this catastrophe could be, and proposed what we could do  to prevent it from happening.

If this were your typical Hollywood movie, the catastrophe would be  something utterly sensational. Like an asteroid the size of  Texas smashing into actual Texas. Or some tech bro’s AI software gaining sentience and starting a crusade against  all life on the planet.

The reality might sound  downright boring by comparison: The scientists were raising awareness  about so-called “mirror bacteria”... a type of synthetic bacteria whose  molecules are all back-to-front. But the threat they pose is right up there with anything Hollywood could throw at us. Intro Jingle

To understand the true threat of mirror bacteria, we have to start with the chirality,  or handedness, of molecules.

All life on Earth is carbon-based. The biomolecules that make up both  you and the oodles of microbes living inside you all feature carbon atoms. And to make molecules, each carbon atom can make up to four chemical  bonds with other atoms.

Sometimes, they bond in such a way  that they create something chiral: you can wind up getting either  “left-handed” or “right-handed” versions of a molecule. Just like your own hands, there’s no way you can  rotate a left-handed molecule to make it indistinguishable  from its right-handed twin. It will always be a mirror image.

But when it comes to very important biomolecules, like DNA or proteins, life needs them to always  have the same handedness. A mixture doesn’t work. So way back in the planet’s primordial soup days, life basically had to pick sides.

In literally every living thing on Earth, DNA and RNA are right-handed,  and proteins are left-handed. Side note: When I say DNA is right-handed, I’m talking about the configuration  of the sugars inside the DNA molecule being right-handed. Not the twist of the helix.

Usually, the helix is also  right-handed, but it can be left-handed. In fact, SciShow’s covered that,  before. But the DNA sugars?

They’re all right, alright? Anyway… our left-handed proteins can  interact with right-handed DNA, no problem. But a left-handed protein trying  to work with a right-handed protein would be like trying to put your  right shoe on your left foot.

The reason we know all of this is scientists can make heterochiral DNA and proteins. In other words, the mirror  versions of what nature churns out. And experiments have proven that  our left-handed protein enzymes mostly can’t react with right-handed  versions of the proteins they’re supposed to.

But this isn’t always a bad thing! Heterochiral components are useful in drugs, because the body can’t break them down as easily. These drugs have plenty of  normal-chiral parts that can interface with proteins in your body, but some of the building blocks are heterochiral so the drug has a longer half-life.

Also, those heterochiral molecules are less likely to trigger an immune response, which is great for therapeutic applications. So drugs of this nature are an active area of R&D, and they’re not considered  a threat to our existence. In fact, one that treats chronic kidney disease is already approved and in use!

And a cancer-targeting one is in clinical trials. But if scientists can already make  heterochiral DNA and proteins, can they use those building blocks to  make something way more complicated? Say, a whole mirror bacterium?

The answer is…not yet. Labs are still working on synthetic  bacteria made out of the regular stuff, let alone the mirror stuff. But once that box gets ticked  off the proverbial To-Do list, it’ll likely be pretty  straightforward to make the jump.

Plus, we wouldn’t need to engineer  a whole mirror environment, including mirror food to sustain  these new mirror bacteria. That’s because a lot of nutrients  aren’t chiral molecules at all. They can be metabolised by  both normal or mirror proteins.

Basically, a future Earth populated  by mirror life isn’t imminent. But the scientists behind this warning  think it’s definitely possible. And there has been some funding  put towards that goal, already.

No, not by a mad billionaire  trying to wipe out everyone so he can reset evolution  on the planet and play god. Although given how we opened this episode, you might be wondering “If  not that, then who? And why?” Well, there’s interest for a couple of reasons.

As far as we know, life evolved  just once on this planet, so some scientists wonder whether  our specific chirality setup is a coincidence that evolution  just decided to run with. If they could create and observe mirror bacteria, they might wind up proving that right-handed DNA and left-handed proteins are actually  better-suited for life on Earth. Meanwhile, there’s also a more pragmatic goal: Remember those next-gen drugs  that are part mirror molecules?

Well, right now those molecules  are tricky to make synthetically, so scientists could potentially use  mirror bacteria as tiny factories. And yet, the authors of that 2024 report proposed a ban on funding  projects to create mirror life, and stringent regulation and oversight  on any research that’s mirror molecule-y. So what has these experts spooked?

Basically, it boils down to the fact  that all our defenses against bacteria are based on chiral chemistry. Just like a left shoe doesn’t fit  particularly well on a right foot, most of our current antibacterial  tools aren’t compatible with mirror bacteria’s biomolecules. Take antibiotics, for instance.

While there are some classes  that don’t care about handedness, most existing antibiotics are chiral. And while it might be possible to  make mirror antibiotics in some cases, it’s neither a quick process,  nor guaranteed to work. Then there’s the human immune system which itself, which relies on recognition to  activate its bacteria-destroying mode.

That’s not an option if the bacterial proteins  are mirrored and effectively invisible to our detector proteins. But even if our immune system  could sidestep that hurdle, to at least figure out that  the body had been invaded, our enzymes that digest bacterial proteins  likely wouldn’t work on that mirror life. And before you think “Maybe Nature has a way to destroy those bacteria  before they get into our bodies!” Well, there are viruses that  help keep populations down.

They propagate by…hijacking the  bacterium’s proteins and then killing it. Yep, it’s the protein problem once again. Bacteria also have predators, but they might not be able to digest  the mirror version of their food.

And bacteria do battle amongst themselves, too. But their weapons are biological in nature, and  they likely wouldn’t work in the mirrorverse. All that’s to say that, according  to this group of scientists, mirror bacteria would be invisible to most natural forms of defense that’s  survived billions of years of evolution.

So the concern isn’t that they’d  cause some kind of disease. It’s that once they got inside you… whether it’s through a cut in your skin  or one of your many mucus membranes… they’d multiply unchecked, and eat  up all the nutrients your body needs. They might even damage your  body due to their sheer mass!

But it’s not just our defenses that  would conk out in this scenario. The same would apply for other animals and plants. So, if an infected human shed some of  mirror bacteria out into the world, you might have to say goodbye to agriculture … not to mention a bunch of living  things you don’t plan to eat.

Maybe human ingenuity could come up  with some sort of countermeasures. We are pretty ingenious after all. But not before a significant loss of life.

And the Report proposes it wouldn’t  be enough to ever stop the damage. They would merely prolong the inevitable. Of course, it’s worth noting  that other scientists have argued all this fear is premature, and bans could stymie unrelated research.

But they do agree with those  38 authors on one thing: it's important that we have a robust  discussion about the risks and benefits of this technology before actually doing it. Meanwhile, if Hollywood wants to make  a movie about a world getting undone by a bunch of microscopic,  mindless, mirror-universe soldiers… I am not gonna watch it That sounds gross [ Outro Jingle ]