Creating a hitman inside our bodies: Killer bacteria discovery could help target disease

Scientists have known for a while that bacteria can kill each other. But new research finds bacteria not only commit murder, but they also can eat their victims. And that could have implications both for us and for the planet.

Glen D’Souza is an assistant professor in the School of Molecular Sciences at Arizona State University; he’s also a faculty member of the Biodesign Center for Fundamental and Applied Microbiomics there.

D’Souza joined The Show to speak more about what he’s discovered about these bacteria: Not only will certain bacteria kill other bacteria, but that they’re also consuming them.

Full conversation

GLEN D’SOUZA: Exactly. They, they have a myriad of ways to kill each other, right? So that's been known, right? That's how we discovered antibiotics, right? That's because one bug was producing something to kill another one in its surroundings.

Now, what we wondered when we started this study was, what, what happens if, if you have all the means of warfare, but you're starting in a situation where you can't grow yourself, right? Because to kill someone, you need to be autonomously growing.

And so when we started looking at starting these bugs that can kill but cannot grow, what we find is, you know, the same things to kill someone else release nutrients, right. So, you know, if you think of it in a very abstract sense, every cell is a pocket of nutrients, right. So there's fundamental things like carbohydrates, proteins, vitamins that you need to require growth, right.

So if you need to access nutrients when you can't grow yourself, you just punch holes in your neighbor, right? And, and these mechanisms are already there. You can always kill your neighbor, and that's what we found in microbial communities.

MARK BRODIE: So it's not so much that they're killing like because they don't like the other bacteria, but it's because those other bacteria have things that the killer bacteria need.

D’SOUZA: Exactly. So there's two circumstances, right. So if, if you have an environment where you can happily grow, you're gonna kill and like plunder, right? You, you're basically gonna remove your competitor away and you get access to their territory of space. That's, that's, that's standard, that's, that was known.

What we now know is if the bacteria in a situation where they cannot grow, they're gonna wait it out and then start killing, but selectively. They're not going to like remove the entire neighbors out. They're going to selectively only kill, punch holes into a few cells, leak nutrients out that in so that it's early enough for them to grow and, and then they can survive.

BRODIE: In the world of what you do, how big of a discovery is this?

D’SOUZA: So we knew these, these systems are, you know, 25% of all bacteria on the planet that we know of have these systems, right? So conventionally, we thought, OK, they have this system, there's this competition, this cooperation, similar to human societies.

What we didn't know for a long time is how do bacteria grow in, in natural environments, right? So, if you think of the desert, like the soil there is extremely limited in what nutrients bacteria can have to grow. If you think of the ocean, there's very little nutrients out there.

If you think of the human gut, right, a lot of pathogens, bacteria that cause diseases have to survive in my body to give me disease, right. Many times my body or my gut will not have the correct environment for these pathogens to survive.

Now what we found is these pathogens have these killing systems, right. So what they can do to survive is kill the good bugs in my body, right, so that's, if you think of it that way, we now have a means of answering, why do bacteria grow at all? Or why do bacteria survive in many such nutrients-sparse environments. So from that perspective, it's, it's quite big, right.

BRODIE: And that would seem to have fairly significant implications, if I'm understanding correctly, for health care, right? For, for medicine, for antibiotics, probiotics.

D’SOUZA: Exactly. So I mean, there's two implications, right. So we always want good bugs to survive. We want the bad bugs to not survive, right. For the bad, so, you know, one thing, you know, you want to eliminate the bad bugs, right. We've historically relied on medicines, or modern medicine, or antibiotics.

Now, what if there are other bad, good bugs that have these killing systems? If you learn how these killing systems work, right, when do you go and hunt? When you go and kill your neighbor? We can repurpose this to go and find the bad ones, right. So you can essentially, use good bacteria that have killing systems to go and find the bad bacteria and kill them, right, selectively.

So that's one. The other thing is the mechanism of killing, right. You can think of a small bacterial cell having a spear gun, right, at the tip of the spear gun is a toxin. But this spear gun, you can leverage to, to inject whatever you want, right.

So you can, you can develop drugs or you can learn what drugs are out there and you can load it on this spear gun, and you can let these good bacteria with the spear gun go and find and kill selectively the ones that are bad. So this is from that point of view, there's huge implications.

BRODIE: It's almost like we're creating like contract killer bacteria, like creating a hitman inside our bodies.

D’SOUZA: Exactly. And these hitmen are there, right. We just don't know what they like, right. So, so right now we're learning, what are the, what are the elements of this contract?

BRODIE: And am I right that there are also potential implications beyond just our bodies you found here?

D’SOUZA: Yeah. So if you think of the ocean, right, if a fundamental process, you know, that's responsible for the Earth's health is this carbon captured by algae, right? Algae fix CO2. They dump a lot of this carbon from the atmosphere into the ocean, and a lot of this carbon then seeps to the bottom of the earth's oceans, right?

This is the carbon cycle. This is very important for the health of, an ecosystem for the, for the planet. Now, how much carbon goes from the atmosphere to the bottom of the ocean. Historically, we just know that there's bacteria that degrade this carbon and that determines this.

Now, we know there's bacteria that are killing and punching holes into other cells, right. And if you kill and punch holes into other cells, you're releasing many more nutrients out, right. So how you're basically, we have to fundamentally ask how much carbon actually has been returned back to the atmosphere and how much carbon goes to the bottom of the earth's oceans.

So, and these killer killers might be, influencing this in, in, in quite a substantial way. We just don't know how much.

BRODIE: When you talk about potential advances in medicine, do you see what you have found here and maybe what it could lead to as a way to counteract, for example, bacteria that are resistant to antibiotics?

D’SOUZA: Yeah. So why are bacteria resistant to antibiotics? There are the major ways, right. So if you think of penicillin, one of the first antibiotics found, penicillin affects the bacterial cell wall, the outside of a cell. It doesn't allow bacteria to build new cell walls. And if you can't build cell walls, you don't have an outer body, right? You just leak your contents out.

Bacteria over time have evolved resistance by changing their cell wall structure so that penicillin doesn't affect it, right. So that's how it works. Now, what if there is no penicillin outside? Bacteria evolve resistance if they encounter this antibiotic.

In these killing systems, that, that toxin is inside of another cell. So most bacteria likely would not see it. Unless another cell comes and bumps into it and injects it, right.

BRODIE: It seems like being stealthy here would be the key. Like, so, so the bacteria almost doesn't see it coming.

D’SOUZA: Exactly. So, so if you don't see it in the, if you create situations where you just inject it at the point of whatever, contact, right. So you don't see it in the environment, that, that is definitely an advantage.

The other thing is, you know, if we try to understand the mechanisms of the contract, we can change toxins however we want, right. There's a million different toxins, right? All we need to do is load different, different weapons, in a bacterial cell.

So there's different ways to play this, learn from what nature has, all the different varieties of toxins and load it. And on the other hand, maybe be stealthy and maybe not use the weapon every time you want. Engineer situations where only certain weapons are delivered.

Given this environmental circumstance, so there's, there's multiple ways to sort of avoid this and reduce the chances of resistance.