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Some species of bacteria have a wicked survival strategy: killing members of their own species or a closely-related one. There’s a lot we don’t know about it, but it's possible that someday we could potentially harness that knowledge to kill them inside the human body!

Hosted by: Michael Aranda

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Sources:
https://phys.org/news/2020-02-scientists-bacterial-cannibalism.html
https://www.mdpi.com/2079-6382/8/4/230/review_report
http://grantome.com/grant/NIH/R01-HL142626-01A1
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6963621/
https://microchemlab.com/microorganisms/bacillus-subtilis
https://www.pnas.org/content/102/24/8710
https://www.sciencedirect.com/science/article/pii/S096098221631003X
https://www.cdc.gov/pneumococcal/clinicians/clinical-features.html
https://elifesciences.org/digests/45257/zooming-in-on-sporulation
https://www.sciencedirect.com/science/article/pii/S0960982215008738
https://books.google.com/books?id=Sq1OBAAAQBAJ&pg=PA212&lpg=PA212&dq=%22blood-air+barrier%22+%22air+bubbles%22&source=bl&ots=eO4aiM-dwX&sig=ACfU3U3D3QPi4RRBKmAWhBV1QTDpwNZzGw&hl=en&sa=X&ved=2ahUKEwj-x5Go_eHnAhW2JzQIHUDwC5oQ6AEwEHoECGEQAQ#v=onepage&q=%22blood-air%20barrier%22%20%22air%20bubbles%22&f=false

Images:
https://en.wikipedia.org/wiki/File:Bacillus_subtilis_Spore.jpg
[♪ INTRO].

When you think about cannibalism, if that's a thing you do, your first instinct might be to think of humans. But it's a thing in other species, too.

And in some of them, it isn't just about turning your next-door neighbor into a tasty snack. Cannibalism can serve practical purposes. And someday, we might even be able to harness it for the good of our own species.

I mean, not human-on-human cannibalism, the bacteria-on-bacteria kind. Some species of bacteria have a survival strategy called microbial allolysis, which basically means they'll kill members of their own species or a closely-related one. Depending on the type of bacteria or its method of accomplishing this, allolysis may also be called cannibalism, fratricide, siblicide, or sobrinicide.

Just to give you some options. Whatever you call it, there's a lot we don't know about it, but we do know that it happens differently in different species. For instance, Streptococcus pneumoniae, a bacteria that can cause pneumonia and meningitis in humans, commits fratricide when it becomes competent. “Competent” is an interesting word choice, because it almost makes it sound like the bacteria developed self-awareness or something.

But actually, competence is when bacteria acquire the ability to take DNA from their environment and use it to alter their own genetics. How this happens varies, but typically, it's in response to a stressful situation, like starvation or the presence of antibiotics. During this process, the competent bacteria release a protective protein, one that acts kind of like armor.

Then, later, they release a toxin that's deadly to any bacterium without that protein; that is, any that isn't competent. It sounds brutal, but the bacteria that survive can take some of the genetic material and nutrients from their newly-dead siblings. And that can allow them to survive starvation or adapt to new conditions.

But that's not the only way to become a cannibal. Bacillus subtilis, a non-pathogenic bacteria found in soil and vegetation, does things a little differently. It commits cannibalism during sporulation, which is a survival strategy that helps it cope with things like lack of food.

During sporulation, the cell produces at least one endospore: a tough, dormant cell that can endure hard times and preserve its parent's genetic material until conditions improve. But that process requires a lot of time and energy, so B. subtilis tries to avoid doing it. And one way it does that is by eating its buddies.

When a group of bacteria starts down the road to sporulation, they'll produce a toxin that breaks down the cell membranes of their sibling cells. At the same time, scientists believe they also produce something that protects them from becoming victims of their own toxins. So they survive, but everyone else doesn't.

This strategy is thought to give the cannibals the nutrients they need to keep growing and delay the sporulation process for as long as possible. So, in bacteria, cannibalism seems to serve a straightforward, practical purpose. It might help you acquire DNA from related bacteria, or it might be a way to get food.

And some species may have other reasons for doing it, like to help prevent overcrowding. But let's be honest: Most of us aren't huge fans of bacteria, hence our antibiotics, so why would we care if they want to cannibalize each other? Well, precisely because of all the antibiotics.

We've overused these drugs to the point where many bacteria have developed resistance to them. So we need new ways to control or destroy large populations of them, such as those causing pneumonia. And because bacteria that cause that particular illness already know how to kill each other, we could potentially harness that knowledge to kill them inside the human body.

So one day, maybe you could take a pill that doesn't just target individual bacteria, good or bad, but instead specifically targets the whole bacterial community that's making you sick. Honestly, though, that's pretty speculative, because there are a lot of complications we'd need to figure out to make that happen. For one, scientists don't fully understand allolysis, and there are a lot of questions that have to be answered before they can make a safe, effective medication.

For example, in bacteria that acquire DNA from their dead siblings, allolysis helps make competent bacteria stronger and more resistant to stress. And in S. pneumoniae, this process actually causes the bacteria to release a toxin called PLY, which damages the delicate cells that line the lungs and transport oxygen into the blood. This lets the bacteria invade the bloodstream, which can ultimately cause a fatal infection called sepsis.

Which is obviously the opposite of what we're going for. So while using bacterial cannibalism as a therapy could be a promising idea, it's a long way from becoming a practical application. But that doesn't mean this research isn't useful.

That shift from thinking of bacteria as individual cells to thinking of them as whole communities is a big one, and could lead to new discoveries about how bacteria work. And when it comes to medicine, for now, we just need to keep being smart about using existing antibiotics. So, don't take antibiotics unless your doctor says so, take your entire course of them, and wash your hands often, so you can avoid picking up those awful little bugs in the first place.

Thanks for watching this episode of SciShow! If all this talk of cannibalism has gotten you wanting more, for some reason, we have plenty more content like this. For instance, you might enjoy our episode about how our galaxy is also a cannibal.

You know, just go from very small things to very big ones. You can watch it after this. [♪ OUTRO].