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Episode 40: From Baking Sourdough To Petting Your Pup: The Microbiome Of Your Home

Rob Dunn | Baking Sourdough To Petting Your Pup | Microbiome of Your Home

Have you ever stopped to wonder what benefit that spider crawling across your bedroom wall brings to your home? Or how your wet, muddy dog contributes to the microbial communities living on your couch -- and in your gut? 

On this episode, Andrea talks to Rob Dunn about how everything from water filters to sourdough bread inform what's taking up residence within your four walls. Rob is a researcher who studies the biology of daily life, and is the author of five books, including his most recent, award-winning title "Never Home Alone.” 

The two dive into why most “spider bites” are actually something totally different (hint: it’s microbe-related!) and why it’s important to let certain creepy crawlies live inside. At the end of this episode, you’ll be looking at your shower head and your floorboards in a whole new light. 

Resources mentioned on the show: 


On this show, you’ll learn: 

  • Differences in ancestral species of microbes compared to today (3:17)
  • Is exposure to various microbes better as a child than as an adult? (5:26)
  • Microbe exposure in home birth vs hospital birth (7:03)
  • Do the strains our ancestors encountered even exist today? (9:07)
  • Does travel help diversify the microbiome? (10:44)
  • Food microbes: where do they come from? (13:31)
  • What happens in the home when a water filter is used? (17:50)
  • How pets change the microbial landscape of a home (19:19)
  • What good are spiders anyway? (22:08)
  • It’s not a spider bite -- what it could be instead (24:12)
  • How many species live with us? (28:03)
  • How to engage with the study of life that’s happening in our homes (30:05)
  • Ways Rob has changed his own home based on his research (33:00)

BIOHM gut quiz 


Andrea Wien: Welcome back to the Microbiome Report powered by BIOHM Health. I'm your host, Andrea Wien. And today we're talking about how we're never really home alone, even during quarantine. My guest is Rob Dunn, a professor in the department of applied ecology at North Carolina State University. He began his career as a tropical ecologist, but now studies the biology of daily life from belly buttons to sourdough bread, and everything in between.

He's written five books for general audiences. Most recently the award-winning, Never Home Alone, about the species that live around us every day. From wild yeast to predatory spiders, the species we share home with are omnipresent. But how do we cultivate diversity in them? What happens, for example, when you bring a dog into the mix? Or what about something simple like a new shower head? I talked to Rob about all of this and more. Enjoy the show. Rob, thank you so much for joining us.

Rob Dunn: Oh, it's a great pleasure to be on the show. I really appreciate you having me.

Andrea Wien: So we've talked on this show mainly about the microbes that live in and on us, but less so about the diversity of our environments. And as you put it, even in quarantine, we're never home alone, which is the title of your new book as well. And I was just telling you before we started recording that I read the book and it has so many gems that we're really going to dive into today to start inviting this biodiversity into your home and into your life. But from a high-level perspective, what are some of the key takeaways or things that were most surprising that you've learned from researching these microbes?

Rob Dunn: One of the key things that shouldn't have been a lesson, because it was obvious in the scientific literature if you looked in the right way, but we're still a surprise as it emerged was that nobody's house, nobody's hospital room, nobody's space station is devoid of life. Every place we've ever looked for other species, there are other species. Every cutting board you've just cleaned, every refrigerator.

And so, that actually has a bunch of implications that are not obvious to the way we think about our daily lives. And so, for example, it means that you're never going to get rid of the other species around you. And so the best that you're ever going to hope for is to favor ones that you like more and disfavor ones that you don't like. In some ways, it's not so radical. But it's not the way we live our lives. And so I think for me that's been a big lesson that's been repeated every time we've studied some new part of the house. And so, it's true of your tap water. It's true of your fridge. It's true under the bed. It keeps coming back at us.

Andrea Wien: Yeah. And I have some specific questions about the spiders and centipedes and things like that that are living amongst us. And every time I do an interview with someone, obviously, I'm looking at it through my personal lens. So, so many of my questions are so personal and a little bit selfish, I would say. But hopefully, other people find some benefit in that as well. So we'll get to that. But we had a discussion with Dr. William Parker at Duke, and we were talking about humans and intestinal worms. And so, we touched on this a little bit. But how different are the species that we're living with and exposed to in our homes today different from what our ancestors may have been exposed to?

Rob Dunn: So they're super different is the short answer. So the study that I like in this regard to the study by Megan Thomas, who's now in San Diego. Megan studied what lives in chimpanzee nests. And so chimps make these nests every night. And it's the closest they have to a home that they get exposed to more. And so she went to figure out like, "Well, what species live in that nest? What are they being exposed to?" And to the extent that anybody thought about it, very much people thought, "Well, it's probably like fecal microbes, dirty chimps."

And she looked and it turned out that what's in the chimp nest is almost exclusively species associated with soil and leaves, and even what's in the air, and on the barks of trees. And so really it's a world of microbes associated with the rest of nature. If you then pivot to think about the average apartment in Manhattan, the average apartment in Manhattan is really dominated by the microbes associated with bodies.

One element of this change is this shift from soil and leaves to our own falling apart. And then in addition to that, there are specific species that we've been associated with for millions of years that we're no longer being exposed to. And so it's a pretty radical change. And I think we've not fully noticed how radical it is. It's true for what's in our houses. It's true for what's on our skin. It's true for our guts. And we're so new to studying. We don't actually even know when that change happened. Is that the last hundred years? Is this something that happened it started 20,000 years ago? But it's a pretty radical shift.

Andrea Wien: Yeah. And I think what we do know, really, and what your book so eloquently showed as well, was that biodiversity and really having as many strains as possible can really help ward off some of these things like allergies and auto-immune diseases that we're seeing skyrocket in places that have great sanitation and great public health systems and all of these types of things. So do we know yet how much more valuable it is to have exposure to a diversity of microbes as a baby or a child versus trying to add those in as an adult?

Rob Dunn: Yeah. It's really hard to add them back in as an adult. And it's hard on two levels. In terms of immune exposures, it seems like it matters a lot more what you were exposed to really in those first years. And I would say we don't totally understand why that is. But it's pretty clear that it's true, even in utero. And so that really early period for making your immune system, allowing it to make sense of the world.

But the other thing that happens, especially for gut microbes, is that after about a year old, our stomachs become really, really acidic. And why that happens is interesting in and of itself. It's really different than other species. Our stomachs are very weird. But once their stomachs become acidic, it's very hard to get new gut microbes established. And so you have this early window that's really very important, which is also just a real downer in the sense that there's already so much stress associated with parenting in those early years. And now you're going to make sure your kids get the right microbes. What a terrible additional thing? But our bodies are our bodies, and we just have to deal with it.

Andrea Wien: That's funny. I actually have an 11-month old baby. So this has been certainly something that's been top of mind for me. I know you talked about in your book bringing pets into the home, which we'll talk about. But we're getting a dog for him so he can have exposure to that, which we can speak about the pros and cons of having pets, which you talked about in the book. But yeah, I mean, even things vaginal birth versus C-section, home birth versus hospital birth, something that people are starting to think a lot more about COVID times. Should I have the baby at home? We know that the microbes are wildly different in the hospital than in our home, right?

Rob Dunn: Yeah. And none of these questions are easy. I mean, every time you…I mean, as you live your own life, each time you ask one of these questions, it's got all sorts of other things associated with it. So you don't get to make it in the abstract. Just this versus that. I've started to think about in the context of bug that if you look at something like a termite, a termite has all these microbes that it requires for its daily life. And it has a very complex system for making sure that they're passed generation to generation, special pouches and special ways of sharing those microbes.

Our bodies have those two. Vaginal birth ensures some microbes are passed onto the baby. But societally, we've not figured out how to ensure it. How do we ensure that our next generation of children that we pass on to them, all of these microbes that they might need? And because our lives now are so different from our ancestral life, we have to think about it consciously. We can't just let it happen the way that it's happened for generations and generations. And so how are we going to do that? How are we going to make sure our babies don't just end up covered in hospital microbes? They're pretty tricky questions.

Andrea Wien: Yeah. And I think this is an exciting time because we're starting to answer them instead of just wondering why babies in hospitals might be getting sick from a nurse, per se, or all these different things. So at least the questions are being asked, which is the first step

Rob Dunn: I mean, we've made so much progress even in the last five years in thinking about these questions and beginning to have some kinds of answers. Why is it that C-section and vaginal-born babies have such different microbes? Why do C-section babies sometimes have microbes that seem really healthy and other times they don't? But I think we're getting much closer to having pretty good answers to some of those things.

Andrea Wien: Now, when we talk about starting to garden these beneficial species in our homes, or increase our environmental diversity and our exposure to that, we talked about our ancestors having wildly different microbes. Do these strains even exist anymore, some of these things we saw in the past? Is it even possible to have the breadth and depth of environmental microbes that our ancestors may have?

Rob Dunn: That's a good question. I mean, I think yes and no. So certainly some of the species we were historically associated with are probably extinct now, some of the strains that were passed from one generation to the next. But the other reality is that our early human ancestors lived all around the world. And so, they were passing different species in different places. And so there are many ways to make our environmental microbes work on our behalf.

And so I think that probably even if some of those microbes were lost, there are others that probably can do a pretty good job. And so, for example, there's been a bunch of recent studies in Finland showing that kids can do pretty simple things in their environment to make sure that they're getting microbes that are associated with better health. And probably those microbes in the Finnish environment are not the same microbes that our ancestors were acquiring in Ethiopia. And yet they still seem to work.

And so I think all is not lost in that sense. And so, Finnish kids can be healthy kids too. And sometimes it's really simple. The Finnish studies show that if kids have more kinds of species in their backyard, and then are engaging with those species, they're working in the backyard, that they then have different microbes on their skin, and they have a decreased risk of allergy and asthma. And so that's a pretty simple intervention. Plant more things in your backyard, go in the backyard more, which I think is actually very hopeful.

Andrea Wien: Yeah. And it begs the question for me. Is travel a way to bring bacteria or microbes home that you wouldn't have exposure to otherwise? Are they likely to proliferate once you're back? I live in Ohio. So back in Ohio, if I've gone to Morocco, let's say?

Rob Dunn: That's a good question. So I would say that as an adult, your gut microbes, if everything is going well, they're pretty locked in. And so unless you get sick, the odds that what you ate and what you encountered in Morocco is going to colonize your gut are pretty low. The skin is a little bit more flexible. We actually did a through time study of students at three different universities and found that the most variable microbiome is the skin microbiome.

And so you might imagine that what you touched and how you interacted in Ethiopia might influence your skin microbiome. The other thing we know, though, are chronic kinds of exposures, and they don't use it in a negative sense, have a big impact on skins. So something you do again and again.

And so we did a study with bakers in Belgium where we brought bakers from around the world together and bake the same bread. And they each made their own starter. And what we wanted to figure out is, do their skin microbes influence the flavor of the sourdough starter that they've made? And they did. Their effects were subtle, but they were there. So you can taste an individual Baker's microbes.

But the thing we hadn't planned on studying that emerged from that work was that when we looked at the skin of the bakers, their skin was covered with sourdough bacteria and sourdough yeast. It was like their bodies have become a giant starter. And so, to me, that suggests that there are these ways that when we take an individual trip that we change our exposures. But at the same time, what's probably a much bigger effect is how do we live or average day?

And that really was a important take on for me because I then came home from that study thinking, "What is the average day for my kids? If that's being recorded in their microbes, what do I want it to say about the days that they're having, the exposures that they're having? And how would I like to change it?" And so I think it suggests that maybe we need more than travel. We need to really think about what our average day is like. And I think this is actually a good time to think about it because we really had to change our average day. We had to change our lifestyles. And as we come out of COVID next year or whenever it happens, what do we want our microbes to be saying about the ways in which we're living?

Andrea Wien: I think you brought up a couple of different points that I want to touch on. Let's stick with the sourdough, because that was such an interesting topic. And it's something I think that so many people are suddenly doing now at home, myself included. I have celiacs. I'm gluten-free. So I think gluten-free sourdough is a little bit more of a project, and a little bit more difficult to get off the ground. But it's been going well. But when I think about where the microbes in our food are coming from, is the sourdough starter, you mentioned hands. But is it coming from the flour also? From the air? What's really happening when we leave flour and water out on the counter?

Rob Dunn: Yeah. So partially the bacteria, especially, are partially coming from the flour. Some of the yeast are coming from the flour. But they're also coming from your body. They're coming from other things in your kitchen. And so for people who bake a lot, yeast just accumulates all over the place. And so there's some of that transfer. It's not coming from the water. So the average sourdough starter has lactic acid bacteria, which make it sour and it has yeast, which make it rise.

And the yeast don't float very well in the air. And so there's these chubby little round organisms. And so somehow they actually have to be touched into the starter. And so they're not so much falling in. And so that's why the hands become a pretty good vehicle for transferring things. Some people actually add other things to the starter that bring the yeast too. But often, it's very, very bodily. And the same for a lot of the other things we make. Like the most common yogurt microbes are body microbes. The yeast that's in beer and wine, that's a body microbe of a wasp. People don't like this, but our food microbes are really very bodily.

Andrea Wien: So because gluten-free bread isn't needed, would you expect to see differences in the hands of gluten-free bakers versus someone who's making traditional sourdough?

Rob Dunn: So I might. That's a good prediction. We've not looked at that. The other thing that's different about gluten-free bread is it provides different nutrients to the microbes. And so you might see effects from that too. I mean, the other thing we think a lot about is like, "Well, what about butcher's hands? Do they have really unusual microbes?"

Andrea Wien: Interesting.

Rob Dunn: Cheese maker's hands must be totally wonderful and unusual I believe. That study's not been done.

Andrea Wien: Then I guess on the flip side of that, if someone had an unhealthy microbiome or skin microbiome, would that potentially make the food stuff less healthy in the end?

Rob Dunn: Yeah. I think there are two ways that can happen. One is that you can have a body microbiome. It's just not very conducive to the starter, like it just doesn't make a starter that works. In which case, you would just have trouble making a starter. You weren't getting colonization from other places. With sourdough starter, it's unlikely it's going to make the starter unsafe. Because once the starter becomes acidic, it's basically safe. That acid being produced by the lactic acid bacteria kills the things you would worry about. And then you're also baking the bread.

But something could be safe and not very nutritious. And so then there's this other question that's there, which is, do some people have body microbes and then sourdough starter microbes that lead to more nutritious bread? That's almost certainly the case. We've never studied that, but it has to be true on some level.

And one cool example that we started to poke around with a little bit is that some kinds of fermentations appear to have nitrogen-fixing bacteria. And so the bacteria actually gathered nitrogen out of the air and bring it into the food. And so after the fermentation, there's more nitrogen in the food than there was before. And so you could imagine that some people have some more of those microbes on their hands, and then might be more likely to make a starter that fixes nitrogen that gathers it. And so there are these extreme cases. On some level, that has to be true, I think.

Andrea Wien: I can just imagine food companies someday harnessing that and saying, "Our bread was made by someone that's never taken antibiotics and has totally cleaned microbiome," and really leveraging that for some type of marketing ploy, I'm sure.

Rob Dunn: Yeah, this is dirty Pete's rock.

Andrea Wien: Yeah, exactly. Exactly.

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Now, in the book, you also talk about the biofilms in shower heads and in our tap water. Our listeners are familiar with biofilms from just talking to other scientists on this show. But what happens when you have a water filter in place that removes things like chlorine and fluoride? Do these species still continue to thrive in our pipes? Would you expect to have different species at that point?

Rob Dunn: Yeah, that's a good question. So we've not studied that. And I don't actually know of any studies of what that does to the biofilms. Just as a little background, what we've seen a lot of is that when you have chlorine in the water system that it appears to favor chlorine-tolerant species that build up in biofilms. And so what you might predict is if you have one of those filters in place is that right before the filter in your water line that you have the build up of chlorine-tolerant microbes, that after it they might become rare.

I think that would be the prediction, but I don't actually know of any studies that have looked at that. Of course, you're still going to have microbes in your water. It's just tipping them from one group of organisms to another. And if the filter like that work to disfavor the chlorine-tolerant microbes, it would be a good example of the ways in which we can garden some species and disfavor others. So it would be a hopeful thing.

Andrea Wien: Certainly. I mean, anecdotally, we do have a whole house filter on our house. And I've noticed that the growth, how you get that pink tinge if you don't clean the shower head regularly, that has pretty much completely dissipated. So it seems like the microbes have definitely shifted from when we had just regular tap water coming into the house filter.

Rob Dunn: Oh, pink tinge? I've never heard about that before. That sounds scary.

Andrea Wien: Sounds like a little moldy.

Rob Dunn: Yeah. I'm just joking. We see a lot of pink tinge.

Andrea Wien: Yeah, yeah, yeah. Now, how do pets, we touched on this briefly, but how are pets changing the microbial landscape of the home?

Rob Dunn: Pets have a huge effect. We see the biggest effect with dogs in part just because there are lots of dogs and they're big. If we take a group of houses, and we want to explain what's the single biggest factor that accounts for the difference between house A and house B and house C, it's whether or not people have a dog. And so for a bunch of microbes, dogs explain about like 40% of the variation house to house in which microbes are present.

And so they're bringing in soil microbes in their feet. They've got farm microbes. They're drooling all over the place. And then there's a hint of dog fecal microbes everywhere. But it's everywhere. It's not just where the dog has been. It's in the dust. It's on the TV. It's on your pillow. And so it's a pretty big effect. And we see a more modest effect of cats. We've not looked at ferrets and iguanas and the like. But the expectation would be that every pet you're bringing in has some effect.

Andrea Wien: And that's not just on the beneficial side of things, right? You also talk about there's pathogenic strains that animals can bring in?

Rob Dunn: So cats rather famously have this parasite, toxoplasma gondii. It's risk is greatest to pregnant women. And so for pregnant women who were exposed to this parasite, it can be very dangerous to the fetus. But it can infect anybody. And it has the unusual characteristic that it alters behavior. And so, it gets into the brain and produces the precursor to dopamine and specific places.

And mice and rats, it's been known for a long time when it does this, it actually makes the mice and rats more risky, actually not afraid of the smell of cat pee anymore, and makes them more likely to get eaten by a cat. And this matters for the parasite because it can only have sex in cats. And for a long time, that was a weird thing in college no one cared about. And now it's pretty clear that it also has behavioral effects on humans. And so, if you have this parasite in your house and you are infected by it, there's some chance it's actually changed in some meaningful way who you are, which is a crazy thing. And nature just does weird stuff.

Andrea Wien: Yeah. And I think the more that we learn about the mind-brain connection, mind-gut connection, we're really learning that microbes they influence a lot of what we think of as ourselves. So this would really just be one more example of that.

Rob Dunn: Yeah, that's right. That's right. I mean, so this is the longer studied version of what we're seeing over and over again, which microbes you have influences how you think, what you crave, what you eat, how good you feel, all kinds of things.

Andrea Wien: So now to switch gears, I know people are going to get a little squeamish to talk of insects and bugs and creepy crawlies at home. But we just moved into an old house and we're constantly finding centipedes, and spiders, and ants. They're kind of a bound in our home right now. So should I be trying to let these things live instead of trying to eradicate them? What kind of spiders?

Rob Dunn: I'm insulted that you think that your listeners will be worried about the spiders but not about your pink shower.

Andrea Wien: They should be concerned about that too, let's be honest.

Rob Dunn: I was talking to somebody the other day and they were asking about the house centipedes. And I'll be honest that my wife does not like house centipedes. And so if I spot one, I move it to a far room. I think one of the questions to ask is, if you see a spider in your house, if you see a house centipedes, they're predators. And so, their presence implies that they're eating something.

If you think about Yellowstone National Park, one of the things we learned in Yellowstone when they reintroduced wolves, is that when you introduce the wolves, the herbivores become less common, the grass has changed, the trees changed. The whole dynamics change. On the flip side, you remove spiders and house centipedes from your house, if you squish them or take them outside, because their presence implies there are stuff that they're eating. What's going to happen to that stuff?

And my experience of talking to people about the species in their house is people tend to like the things that house centipedes and spiders eat even less than they like the house centipedes and the spiders. That's one way to think about it. If they're already doing this service for you, let them be and do their good work. And then there's other cool stuff in your house that you're not even noticing but benefiting from. Almost every house we've looked then has a little teeny wasp that's like half a jellybean length and size. And it lays its eggs in the egg cases of cockroaches where they then eat the baby cockroaches alive. So how could you not like that and want that in your house with you keeping things in order?

Andrea Wien: Yeah, they sound pretty gnarly.

Rob Dunn: And they're teeny. They're like little robots.

Andrea Wien: That's so funny. I liked in your book too, you said that every year there's tens of thousands of spider bites that are reported around the world. But you're saying spiders rarely bite humans. And most of those bites, if not all, are actually due to staphylococcus bacteria, so MRSA. Can you talk a little bit about that?

Rob Dunn: Yeah. So if somebody comes to me and says, "I've got this gnarly spider bite, that won't go away," I almost always send them to go get a check for MRSA. I mean, it's by far and away, in my experience, the most common "spider bite." And actual spider bites are really rare. There's been a couple of studies where spider biologists have tried to figure out what do you have to do to get bitten?

The old studies showed they just poke the spider until the spider bit them. And now that's done more subtly. And so they take a stick and they poke it until the spider bites the stick. And the truth is even with the spiders, people are most worried about like black widows, it takes a lot of pokes until the spider will bite, because the spider's first response is to walk away. The second response is to hunker down.

And it's only after you're really gotten very pokey that the spider will bite. Spider bites are very rare. Brown recluse spiders. There are lots of good data showing that people can live in houses with hundreds of brown recluse spiders and never get bitten, which is not to say spider bites never happen. If you're thinking medically, they're not the horse. They're the zebra. They're not the common thing. They're the very rare thing.

In contrast, having a MRSA infection that shows up and it looks like this little bump and you don't remember where you got it, that's the horse. Super common. And I actually think one part of this is I like spiders. I would like people to be more comfortable with spiders. But the other part is it's really important that if you think you might have MRSA to get diagnosed. And so I think that failure is also serious medically.

Andrea Wien: I mean, if MRSA is so common, how are people most likely contracting it then?

Rob Dunn: Yeah, tricky question. I mean, people get MRSA in hospitals. It's a very common place to get it. There's community-acquired MRSA. So MRSA is a staphylococcus strain. And so your skin is covered with staphylococcus microbes. It's not what your ancestors skin was covered with, but it's what most of us have now. But some of the strains of some of the species of staphylococcus can become problematic and cause infections. And so MRSA one of them.

And MRSA is extra problematic because it's resistant to one of the most common antibiotics. And some of the strains and MRSA are resistant to many kinds of antibiotics. And so, people are acquiring this microbe in some aspect of their daily lives. It's a tricky one. And it's one I worry about right now because the more we use antimicrobials and the more we use antibiotics, the more likely it is to be favored, because it's typically not actually that good of a competitor. But the more we clear out other bacteria species on our skin, in our daily surfaces, the better the odds that it's going to survive.

And so just as a weird anecdote, I have a colleague who works on pig farms. And he's found that one of the places that he sees tons of resistant antibiotic resistant bacteria on pig farms is the floors that are actually super duper clean and bleached all the time. And that's because those bacteria then have no competition on those surfaces, and they just hang out and love them. We need to keep washing our hands with soap and water. We needed to keep being very aware of COVID because it's only just beginning. But I think we also need to keep an eye on these MRSA cases and see are we going to be looking at a bunch more than we had before?

Andrea Wien: Yeah. It's definitely a concern. We had a whole episode on immunity and talked about just washing with regular soap and water is really still the best way and staying away from the Triclosan and all of these antibacterial products that are coming out. And just going back to good old fashioned soap and water is what works best.

Rob Dunn: Yeah. I 100% agree and I have no stock in any soap company.

Andrea Wien: Now, when we think about how many species we're really living with in our homes, do we have any idea what that number is?

Rob Dunn: No, we have no idea. I mean, we've worked a lot in houses in North America. Species we've found in homes were up around a total of like 200,000-ish, depends a little bit on how you count. But globally, what is the number look like we have no idea. And if we think about homes and the tropics, we're going to be seeing totally different species. Matt Baton, who we work with a lot, surveyed a house in Peru. And in that house found a totally new genus of beetles. And it's not even a species. It's like one branch thicker on the tree of life in somebody's kitchen.

When you think about bacteria species, we've named thousands of bacteria species. J Lennon, one of my colleagues, recently estimated that globally there might be trillions of species, which I think is high. But we're so ignorant still that we can't even really convincingly argue that it's too high. And then you've got things like nobody's studied as far as I'm aware of bacteriophages in houses.

And so bacteriophages are these viruses that attack bacteria. And so if you look in your yogurt, your yogurt has yogurt bacteria but also as these viruses that attack the yogurt bacteria. And so, it looks like there's more or less a one-to-one relationship between bacteria species and bacteriophage species. And so if we're finding 80,000 bacteria species in houses, does that mean there are also 80,000 bacteriophage species? It's really we've just cracked open the window onto this world just a teeny bit. And we have so much to study that it's impossible even to think about how do we move forward? There's just so much. Yeah, we don't really know.

Andrea Wien: I'm just thinking it doesn't even seem possible that that would be answered in our lifetimes. It just seems so vast. But I don't even know how you could catalog all of it.

Rob Dunn: Yeah. So I should have just said I don't know.

Andrea Wien: No, I liked your answer better.

Rob Dunn: All right.

Andrea Wien: So aside from people leaving spiders in peace, and not using antibacterial products and things like that, how can people more directly engaged with the study of life that's happening in their homes?

Rob Dunn: We have a couple of projects. We have a project called Wild Sourdough where people can make sourdough bread at home and help us study the biology of sourdough starters. So if you go to our webpage, maybe there's a link to it, but it's just You can find that project. And so it's just a project where you make a new starter at home, and you characterize its aromas and how fast it rises, which will help us to understand do some climates favor better sourdoughs? Do some ingredients favor better sourdoughs? How do you produce a sourdough with really unusual aromas? That kind of thing.

And so that's one. Another one is we have a project on the iNaturalist platform. And it's called Never Home Alone, so if you liked the book. So if you go to iNaturalist and type in Never Home Alone, it's a project where you can just take pictures of the species that you see in your house. And those become data for us to help understand what lives in houses. And at the same time, the project helps you to identify them. And so if you look in your bathroom and you're like, "Oh my God, what's that? It's like half goat, half spider, half wasp."

Andrea Wien: I'm moving if that happens.

Rob Dunn: I mean, it could be small. But take a picture of it and…I mean, fairly high proportion of the time we're seeing things that we didn't know lived in a particular place or even new species. But you take a picture, you upload it and then we help you figure out what it is. And so, if you've got a goat wasp, spider in your house, we want to know about it.

Andrea Wien: All right. We'll start sending. And we'll certainly link to all of that in the show notes It did make me think when you were just talking about the sourdough starters, to get more diversity would it make sense to store them in different places around the home or even in different homes in your mom's house or my sister's?

Rob Dunn: I think so. Although after a while, sourdough starters become stable. And once they're stable, they seem to more or less keep their microbes. The microbes in them are still evolving relative to each other. They're losing genes. They're mutating. But they more or less have their merger. And so I think once they're stable, you can keep them side by side and they're probably they have their identity. But when they're forming, it might be useful to put them different places to make them.

And to put one outside, put one in the attic, put one at your cousin's house as they're forming and they'll likely to end up very different. And then you can bring them all back together so they can live side by side, although that ends up being a lot of work. We do see cool things though in Australia. There seem to be fungi and some of the starters that we don't see anywhere else. And so, it's possible that different places can make really different starters.

Andrea Wien: So doing all of this work, what are the ways that you've changed your home life since writing the book and learning about all these different things?

Rob Dunn: I mean, our kitchen is way more fermenty. The fridge is way more fermenty in part because I've seen the value in having these living foods around us. And part also, because as we've worked more and more with people who do a lot of fermentation, it's just really clear that it can be a very rich part of daily life, a very rewarding way to engage species that we don't see. And so that's been a nice thing. There's more of that.

And also way more aware that when we don't spend much time outside, the microbes on my skin, on my kids' skin are recording that. It's reminded me to get outside. It's reminded me to spend time turning over logs and waiting through streams. It's reminded me of how unusual the indoors is.

And I would say that this COVID time has been an extra reminder in that way. And that we've been spending even more time outside than we usually do. And that's actually a great part of this time, to be outside enough that I'm seeing species in these last weeks that I've not seen in years. And so I think there's that part too. For as much as I studied the indoors, a lot of the time it's reminding me to go outdoors.

Andrea Wien: Yeah, that's a great tip. We'll wrap it up there. Thank you so much for coming on the show. We'll definitely continue to follow your work. You seem to have a lot of different passions and follow them down the rabbit hole. So we like people like that. So hopefully we'll have you back on in the future and we can talk about your new research. And we just thank you so much for coming on.

Rob Dunn: Oh, thank you so much. I really had a good time. And thanks for all the work you're doing.

Andrea Wien: As always, thanks so much for listening. Head to That's B-I-O-H-M, And click on the podcast tab for the show notes for this episode. This episode has been powered by BIOHM Health, a leader in gut health and microbiome testing. Until next time, I'm Andrea Wien.


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