The social lives of bacteria

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1:00I'm a biologist and have spent many years of my life studying tiny fruit flies in the lab. But recently, within the scientific community, there's been a lot of buzz about the social behaviours of much smaller creatures, bacteria. Bacteria are everywhere. They live among us and inside us. And although made up of a single cell, they behave in all sorts of surprising ways, from killing family members to blowing themselves up for the collective good. We have these incredible examples of almost time travel.

1:35Dr Sally Le Page:You might get certain members in the population that actually become cheaters. It's a bacteria warfare on their feet every single second. They change what behaviours they carry out based on whether they're around friends or enemies. Understanding the behaviour of these microbes helps scientists fight disease. and later I'll be visiting a lab at the forefront of this battle. Prepare yourself for a weird microscopic world and the social lives of bacteria. Just like human beings, bacteria are capable of a whole range of unusual and often contradictory behaviours. Unlike us, they split themselves in two to reproduce and have a lifespan ranging anywhere from 12 minutes to millions of years.

2:23Professor Bonnie Bassler from Princeton University in the United States. Bacteria are the world's first organisms, so they're the most ancient critters. They are more different from each other than we are from a yeast, for example, or from a dog or from a plant. And they are all single-celled organisms, and they typically just have one piece of DNA that encodes all of their genetic information. And then roiling around inside these cells, besides the DNA, are all the molecules that make them alive. And if I was to shrink myself down to their scale, what would they look like? Typically, they would look either like spheres or like rods.

3:05And then very often, they have decorations on their surface, like they will have what we call a flagellum. You can think of it as a tail. It's a propeller that helps them go from here to there. They have sort of hairs that hang off the edges of the cell that help them stick to things. So they have features in and on them that give them skills. If you look at them, they actually look kind of the same, you know, these sort of boring, simple, single cells. I've heard them described as physically simple, but chemically complex. Exactly. They are the world's best chemists.

3:41Dr Sally Le Page:The one that probably is my favourite bacterium of all time is one called Pseudomonas aeruginosa. Joe Fothergill is a professor of medical microbiology and director of the Microbiome Innovation Centre at the UK's University of Liverpool. Now, not many people can say that they have a favourite bacterium. Why is Pseudomonas aeruginosa your favourite? I think it's because it's really good at surviving in all sorts of different environments. It is really persistent and it is really adaptable. I always find it interesting that in people, those are considered really positive traits, but in something that can cause infection, then that becomes really problematic.

4:21Dr Sally Le Page:It's also what we call an opportunist. So when there is a breach of the existing barriers, things like maybe a wound or maybe an underlying condition like cystic fibrosis. It is very, very good at getting in and causing infections that are very, very difficult to treat. In fact, many bacteria, like Pseudomonas aeruginosa, often have a very particular set of skills. One of their more social ones was discovered only relatively recently. Bonnie Bassler. Bacteria have been known for 500 years. And for 470 of those years, it was always thought that because they're so primitive and simple-seeming, these itty-bitty, puny, single-celled organisms, that they could not have the wherewithal to do anything except act as loners, these asocial loners.

5:12Now what we know over the last 30 years is that nothing could be further from the truth. They have the capacity to communicate. Their words are chemical. They can count their numbers, and they can recognize when they have the right number of cells in the vicinity. If they all do something together, like an army, like a team, they can accomplish tasks that they could never accomplish as individuals because they're inconsequential as single cells. So this process of communicating and orchestrating collective behavior, we call it quorum sensing. Not only can they tell that there are other cells around, they can actually tell something about who those cells are.

5:55So what they can do is they can tell whether they're surrounded by friend or foe, kin or non-kin, and then they change what behaviors they carry out based on whether they're around friends or enemies. And so that to me sounds very human too, right? Right. It's amazing to think that these bacteria not only have social lives, but that they can cooperate as well. Do they only cooperate with their own species or do they ever talk and cooperate with different species? The latter. They cooperate with other species because they get more bang for their buck that way. So, for example, you know, in the morning you have this goop on your teeth, right?

6:34And you brush it off. That's called a biofilm. There are 600 species of bacteria in that biofilm on your teeth every morning, you brush it off. The next morning, it's back and the organization is the same. The first bacteria that get on there have the capacity to stick to your teeth, but they don't have all the enzymes needed to degrade molecules that help them to flourish. So the first set of bacteria do jobs A, B, and C. The next set do D, E, and F. the third seth do G-H-I, but then together the entire community flourishes because each of them does different jobs, but they rely on each other the same way we do in cities where there's the banker and the grocer and the librarian.

7:17The whole community flourishes because we get the benefit of one another's work.

7:21Dr Sally Le Page:It's coordinated behaviour. You might want to think about people living in a commune where their actions are for collective good, or maybe like a group chat where your communicating with one another and then all deciding to do something, maybe like a flash mob, and then you take everyone by surprise. That's actually really beneficial because it means that in the context of infection, you can kind of be quite quiet and under the radar while you're building up those numbers. And then all of a sudden, you make yourself known when there's enough of you to maybe win that fight with the immune system and establish you there.

7:59Dr Sally Le Page:What I find really fascinating is that there are really complex dynamics even within that population. You might get certain members in the population that actually become cheaters. They switch off their ability to make that molecule, make that signal, but they can still benefit from everyone else making it. It reminds me of people lurking in the group chats. They might not be contributing, but they're still benefiting from all the others contributing. It turns out Joe's favourite bacteria is effective as both a solo agent and a team player. Unfortunately for us, effective means making us ill and resisting antibiotics.

8:38Pseudomonas aeruginosa's group behaviour, however, combines Lord of the Rings with Game of Thrones and, assuming you have the stomach for it, is magically inventive. Its special skill set includes a strong defensive outer membrane.

8:55Dr Sally Le Page:It's like a shield that protects it. When we think about other bacteria, and one you may have heard of is E. coli, its Pseudomonas aeruginosa shield is 10 times stronger than that. So you can really consider it to be this hero superbug with this super shield on the outside that makes it very, very difficult for things to get in. Another way that it can resist antibiotics is that it has pumps, and they can either start or they can start working faster when it detects that antibiotics are there. And that's all things that it can do on its own. Is there any strength in numbers? Absolutely. It can live as a biofilm.

9:32Dr Sally Le Page:And what that means is that it sticks to any sort of surface or component in the lung. It starts building up its numbers and starts covering itself in this sort of gloopy, sticky, matrixy cover that means that it's very, very difficult for the immune system or for antibiotics to really get a hold and kill it in any sort of way. So now they're working in 3D space and if the antibiotic can kill the ones at the surface, the ones underneath, what, protected by the dead bodies of their friends at the top? Yeah, exactly. So even if there is some activity at the outer edge, the top of the biofilm, it's very, very likely that there will still be survivors or persisters deeper down.

10:16Dr Sally Le Page:That is grim, but incredibly ingenious. The other thing is that those dead bodies, they often release DNA, which then becomes incorporated in the biofilm, and the nutrients from those bacteria that are released are also taken up and used by the biofilm. So yes, nothing goes to waste. Oh wow, so they're living in a castle, a highly defended castle. The walls built of their fallen comrades, and individually wearing a magical wizarding shield that stops anything else from getting to them personally. Absolutely. That is insane.

10:53Not all bacteria are so harmful. Pseudomonas protogens is also found in soil, but unlike aeruginosa, it has a more beneficial effect, only this time for plants. Senior scientist Dr Jordan Vacheron from Lausanne University in Switzerland. This pseudomonas is able to protect plants from harmful microbes, specifically fungi pathogens for plants. So this is a good guy? Yeah, a good guy within the soil microbiomes. Since it's a soil bacterium, it will be attracted by the plants at the level of their roots. So plants, through photosynthesis, so they're using the sunlight to produce sugar amino acids in the leaves, and then they redistribute this food through the entire plants.

11:38And since it produces a lot and a lot of foods, there's a lot of leftovers that are exuded from the roots to the soil and then it will attract specific microbes. So it's a kind of buffet for soil microbes. Now, I know that when I go to a hotel and there's a breakfast buffet in the morning, everyone's eyeing up the best bits at the buffet. Everyone's eyeing up the fried eggs and the sausages and the bacon. So is there a lot of jostling around the roots to try and get the best compounds? Yeah, and you have to compete for that. and to outcompete the others. So it's a real, let's say, war within this root microbiome for food and space.

12:14Okay, so it may be a good bacteria, but it still likes a fight. You're listening to this podcast, so I know you've got a curious mind. Here's a helpful fact you may not know yet. Drivers who switch and save with Progressive save over$900 on average. Pop over to Progressive.com, answer some questions, and you'll get a quick quote with discounts that are easy to come by. In fact, 99 % of their auto customers earn at least one discount. Visit Progressive.com and see if you can enjoy a little cash back. Progressive Casualty Insurance Company and Affiliates. National average 12-month savings of$946 by new customers surveyed who saved with Progressive between June 2024 and May 2025.

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13:26I'm Dr Sally LePage and this is the documentary on the social lives of bacteria from the BBC World Service. I'll admit if I'm at a buffet sometimes the elbows will come out but Pseudomonas protogens bacteria have a powerful weapon that will target far more than anyone who gets in the way of that last piece of bacon. It will attack let's say bacteria that are super closely related So we can call them cousins or brothers and sisters as you want. Why are they fighting their own family? The analogy there is like the mafias. So you got different members of the same family that will compete for resources.

14:08But for bacteria, the resources is space and food. For example, they are able to metabolize the same sugar. So eating the same food that you prefer. So they need to outcompete if the food is not enough for everybody. But then they got still kind of different weapons that they can use to ward off their family. Tell me more about these weapons. For example, there's what we call telosynes, which is a derivative of a virus. Under the microscope, it looks like bacteriophages, which is a kind of syringe. So it will contract and inject a tube, so drill into the cell. And you can imagine what thousands of this kind of weapon can do on the cell surface of the bacterium.

14:49So it will burst at the end, the competitor. So your protagines is fighting for sugars at the surface of roots. And you're saying that it blows itself up in order to release these weapons to kill their cousins. Yeah. So there's several individuals within this microcolony that will sacrifice themselves to prevent an invasion from a cousin or sister brother bacterium, let's say. That is such an extreme behaviour to kill yourself. If we're going back to the hotel buffet analogy, I mean, I really want those eggs, but I don't want them enough to kill myself. So what is the advantage of killing yourself just so that you can kill some cousins?

15:34It's kind of sad saying like that, but you just repel your competitors by killing some of them and just showing where the borders are. These are like soldiers that are just doing whatever it takes to protect the colony. Exactly. What was it like when you first looked down the microscope and saw these bacteria blowing themselves up to release these weapons? It was amazing. It was amazing because it was like a firework. So you can see the bacteria that is growing and growing, getting bigger and bigger until it will just burst and release like a firework, all these small particles that are actually the telecines.

16:14I mean, this sounds pretty brutal, right? Yeah, it is. It's a bacterial warfare on their feet every single second.

16:26Dr Jordan Vacheron. Pseudomonas protagens isn't the only bacteria whose actions give us a helping hand. During an oil spill, the numbers of Alcanovorax bacteria skyrocket. They produce a biosurfactant to break down the chemicals in the oil, just as washing up liquid cleans a greasy frying pan. They also work together in biofilms to change the shape of the oil droplets, so their social actions help clean up a disaster more quickly. Professor Lars Blank at the University of Aachen in Germany studies these oil-guzzling bacteria, but he's also interested in what bacteria do when they're stressed out.

17:08When it's too hot or there's no water, some bacteria form spores in the same way as fungi to protect their DNA. It sounded like putting on a protective suit and entering an underground bunker. I like your description very well, but there's one particular challenge for them. They're metabolically not active. So they're not eating. They're really in this bunker. I like that. So you do nothing. You just wait until the conditions outside are changing to the good. Hibernating. I'm sure I've seen films where people are traveling across the universe and they put themselves into these stasis mode, into these pods where they don't have to breathe, don't have to eat, so that when they get to the other side, when there are favorable conditions, they can wake up again.

17:57Yeah. And we have these incredible examples of almost time travel. This is very prominently every now and then in a headline in an Egyptian tomb, where for thousands of years, there was no sunlight, not even some water molecules in a fresh air coming into these rooms. And people then off the walls of the artifacts they find there, they can reawaken these spores to full bacteria or fungi. Hang on a second, Lars. Hang on a second. Are you telling me that there are bacteria that are thousands of years old that went in at the time of the mummies that we are now reawakening into the world? That sounds like a horror film waiting to happen.

18:45No, no, no. This is not a horror film. You will find the same in very icy places where you have very old eyes. There will be also spores because they're so light. We have them all the time in the air. So they will be frozen depending on the age of the eyes. And for us scientists, this is exciting because species can be checked. Did they develop in evolution in these thousands of years or are they still the same? Hmm, I'm still not convinced. Sounds a little bit too much like a bacterial Jurassic Park to me. But what a skill for bacteria to have, time travelling in stasis. Although producing spores isn't the only way to negotiate life's hardships.

19:32Some of the species, for example Bacillus subtilis, has a very tricky social strategy because of the population. Some go for the spores, Some just hang around and hope for the best, that there will be more food, there will be more water. And some, they just lice. What do you mean? They digest themselves. Kill themselves. They kill themselves. And even more, what they do is they chop itself up. But instead of a big chunk of meat, they are nicely cut for their friends to eat them. So this is like being stuck on a desert island with your family. and rather than everyone trying to pick who they're going to cannibalize, one person just puts their hand up and says, hi, don't worry, I'll just kill myself and you can all eat me.

20:21Yeah, I'm not sure if I like this analogy, but yes, one guy cuts itself and that the others can live on it and one goes into the bunker and doesn't move and hopefully keeps less calories and the other guys are still trying to catch the fish and hope for the best that the coconut is growing fast enough. Absolutely. That almost makes bacteria sound altruistic, because while some species will happily go to war to survive, others will sacrifice themselves for family. When modern medicine is faced with that kind of evolving bacterial defence system, it's no wonder scientists face a constant battle to combat disease.

21:04an analysis of diseases in 2019 found that bacterial infections were linked to over seven and a half million deaths every year that's one in eight deaths worldwide there are numerous facilities around the world researching bacteria and diseases including why they become resistant to antibiotics the uk health security agency here in london is one of them hello can i help you we're here to speak to colin brown okay i'll contact him and ask him to come over thank you dr colin brown who's in charge of antimicrobial resistance led me to one of the labs on site after a safety briefing i was shown a kaleidoscopic array of circular plastic containers filled with agar jelly made from algae.

21:55These are used to grow and identify bacteria from samples taken from hospital patients. Oh, we've got a whole selection box of Petri dishes here in colours I have never seen before. So I'm used to this colour, which is just plain and translucent, but you've got a light blue, a very vivid red, a kind of chocolate brown, and then maybe a wine-coloured one. These are just different types of nutrients depending on the type of bacteria that we grow. The green one in particular grows organisms from our gut. Things like Pseudomonas were growing it, E. coli were growing it. Many you'll never have heard of, like Cetrabacter or Scericia or other things with colourful names.

22:31Then we've got the blood agars. That is redder than normal blood though. Well, it's blood with nutrients. And this is chocolate agar, which sounds really nice and it's got a deep chocolate colour, but it's chocolate because it's got cooked blood in it. Oh, delightful. So what would you expect to grow on the blood plates? So the blood plits, we could grow Staphylococcus aureus. We could grow group A streptococcus. These are nasty skin infection bacteria. That can get into the bloodstream and really cause havoc. So if I show you what we would do, for example, let's imagine I've received your swab from the post.

23:06So we undo it. We take the eye. And then it's pretty simple and straightforward. You're unscrewing the swab from its little container. I'll just use the chalkboard as an example where we can just lift it up like that. and then we will do a big swab at the start so we get the bulk of the bacterial contamination there. You're just touching the end of the cotton bud just very lightly on the surface. That's right. And then what we will do is we will streak it out separately until in the end we're left with just a tiny squiggle of a line. And what we hope is we've got the big bit of bacteria at the start and then as we drag it through the different pools along to this tiny line at the end, we will get smaller and smaller amounts of bacteria so that we'll get one that we'll just be able to then take and do further testing on.

23:49And it's that bacteria that we will then grow up in special different types of plates so we can see how they interact with the antibiotics. Bacteria are very social in that they live all in various, what we call dirty bits of the body together. So our gut is the typical example. And through sharing bits of genetic information, I mean, essentially, through the equivalent of a sexual reproduction, they can share genetic bits of code that tell the other bacteria how to be resistant also. And that is the big, big worry. So not just the Staphylococci or the E. coli is affected, but the E. coli share with the Pseudomonas, which share with the Scericia, which share with the Citrobacter, which share with the Enterobacter.

24:27And suddenly you get the whole gut flora becoming resistant. So different species can not only talk to each other, but trade war secrets with each other, trade weaponry ideas. Yeah, absolutely. and they can also potentially trade virulence factors so they can also trade genetic bits of information that tell them how to be more aggressive and then there is a scenario in hospital in particular where we have clostridium difficile or now called closteroides difficile which is a bacteria that can live in certain people's guts but it particularly when we've been given antibiotics which wipe out some of the good bacteria see that space and go ah that's a nice place to live and they suddenly explode in growth and they can take over a lot of the bile sort of real estate that was occupied by the the other bacteria and they can in particular produce toxins that are really aggressive nasty cause very bad diarrhea really quite debilitating symptoms and and severe gut inflammation and even death in some people are they the ones that people are now getting fecal transplants for that is absolutely right fecal transplants are essentially where we choose what we think is a, in some case, a representative sample of healthy bacteria from an individual.

25:44And we, through a safe mechanism that bypasses the stomach and gets right into the gut, transposes that bit of gut flora from the healthy individual into the person who's got either Clostridium difficile or a very unhealthy selection of bacteria living in their guts. And we hope that those take over and therefore they go back to having a normal gut health. So those good bacteria are better at taking up real estate than the bad bacteria, and so they out-compete it. That's right, they're the good neighbours, the ones that bring you over tea and biscuits rather than the ones that aggressively invade your garden.