FLORA LICHTMAN, HOST:
This is SCIENCE FRIDAY. I'm Flora Lichtman, filling in for Ira Flatow today. If you could count up all the bacteria in your house, how many different species do you think you'd find - 50, a couple hundred? How about thousands, with an S at the end? My next guest had volunteers swab surfaces in their home - pillowcase, the TV screen, the toilet seat - to see what might be living there. And in each of the 40 households, the same spots were swabbed.
And what was the result? Almost 8,000 different kinds of bacteria, making themselves at home. Reaching for the antibacterial spray? Well, not so fast. Having all these bacteria is a good thing, my next guest says. We should be tending our diverse microbial gardens.
Joining me now to talk about the microbes we live with, and where they may be coming from, is my guest. Rob Dunn is a biologist at North Carolina State University. He's also the author of "The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today." Welcome back to SCIENCE FRIDAY, Dr. Dunn.
ROB DUNN: Oh thank you so much, Flora, it's great to talk to you again.
LICHTMAN: So it's a biodiversity hotspot in people's homes, it sounds like.
DUNN: It's incredible. I mean, there's life everywhere. It's sort of a thick layer of life that coats everything you touch every morning, every afternoon, everywhere you sit. In the perspective of exploring biodiversity, it's great news.
LICHTMAN: Why is it great news?
DUNN: Well, so our bodies and our health and well-being depend upon the microbes that we encounter in our environment and the microbes that live on us. And so the more we understand the species that live on our bodies and around us the more it seems like having a richness of those species, a diversity, is actually the better scenario.
And those cases where we have few species tend to be cases where we're sick, and so if you have very few species in your gut, for example, it's more likely to be under the scenario where you have a severe pathogen in your gut. And so one of the questions is what is it like when you have very few species in your house. Is that also a case in which you really have a less healthy house?
We don't know that yet, but we're just beginning to study what's there in the first place, to begin to take the steps that would ultimately lead us toward understanding those broader sorts of questions.
LICHTMAN: Let's talk about what you found. Were there distinct habitats?
DUNN: Yes, so in any individual house, we kind of found three major kinds of habitats, much like you might find in Yellowstone or something, except that in your house those habitats sort of ally with where species come from. And so in the kitchen habitat, you tend to have species that depend on our food, and lots of those are species that depend on the plants we eat.
And then we also find a kind of habitat that's associated with species that come in from outside, and so we see those on the outer door sills of houses and then also on the inner door sills and presumably sort of around the house in general as you move in.
And then one of the more interesting habitats is the habitat associated with our bodies physically go, and so that includes our pillowcases, it includes our toilet seats, and we didn't study these other places, but I suspect it also includes our couches, our beds, all those places we plop down.
LICHTMAN: I want to drill down on these places where we plop down. Is it true that you can't tell the difference, microbial, between - microbially between a pillow case and a toilet seat?
DUNN: Yeah, plop down was probably a poor choice of words.
DUNN: But so yeah, so toilet seats and pillowcases are very, very similar. We tend to find more species associated with our mouths on pillowcases and more species associated with feces, with gut microbes, on toilet seats. But in any given house we might or might not be able to distinguish those two. And in general, you know, these places that we sit, that we lay down, they sort of fill with species that fall off of us, you know, biased in one way or another toward a specific part of our body.
But it's kind of this mark we leave on the world everywhere we go, and presumably it's the same on planes, it's the same in our cars.
LICHTMAN: It sounds like our dogs leave a mark, too.
DUNN: Yeah, so one of the really interesting things for us was to try to figure out what explains why your house is different from my house, why any house is different from any other house. And there are lots of things that you can imagine might be important, you know, the size of your house, your air conditioner, the number of people in your house, whether you're a vegetarian.
And so in these first 40 houses, and I should say this is part of a much broader project funded by the Sloan Foundation where we're sampling 1,300 houses, but so in this first 40 houses, we didn't actually expect to be able to explain very much. But then we looked at the dogs.
LICHTMAN: And what did you find?
DUNN: And so dogs explain about half of the variation in the composition of microbes that you find on TV screens and pillows. And so we can actually, with a fair degree of accuracy, predict whether or not you have a dog based on which microbes are in your house.
LICHTMAN: Is that just because dogs are bringing in more stuff from the outside?
DUNN: So it seems to be a mix. So we see a whole bunch of kinds of bacteria that are much more common in dog houses. And some of those are associated with dogs' mouths and noses. And so we see those on pillowcases. You know, that's where your dog's nose is ending up if it's sleeping with you or sleeping there when you're not home.
We also see things that we think are associated with dogs' skin and fur, and then we see soil bacteria that presumably are coming in on their feet. Interestingly, we - although we see human fecal microbes all around the house, we don't tend to see things that we would associate with dog feces. And so to the extent that someone's pooping in your living room, it's probably somebody in your family.
LICHTMAN: Well, that's good to know. So does that mean that dogs and other animals have their own specific set of microbial cohabitants that live on and with them?
DUNN: Yes, so the microbes that live on our body are very much shaped by our evolutionary past and our genes. And so if you were to do an evolutionary tree of the microbes that you find on different organisms, to some extent it matches the evolutionary tree of the hosts themselves. And so we would expect different primate species to have microbes that are more similar to our microbes and dogs to be a little bit more different and so on.
And in part that's because our bodies are very actively favoring some kinds of microbes over others in many different ways. And so for example, in our armpits we have these glands called apocrine glands. And their sole function appears to be to provide food to bacteria. And so the odor that comes from stinky armpits is actually our apocrine glands giving food to these bacteria, which then produce stink.
And the fact that a gorilla smells different from you is because it's feeding different bacteria. The fact that your dog smells different from you is the same.
LICHTMAN: Does that mean that deodorant is a microbial, it's a microbial massacre when you put on deodorant?
DUNN: Yeah, so we're actually studying that to some extent, and it's not super well-known, but the idea behind antiperspirant in particular is that it's creating conditions that make it harder for those microbes to grow. And so what antiperspirant does is the metals in the antiperspirant actually go into the cells in the armpit and make those cells fill with enough water to actually close the pores.
And so it's very likely that what's going on in armpits is very, very different in people who use antiperspirant.
LICHTMAN: Let's talk about the home a little bit more. Is there evidence to suggest that it's better - it really is better to live among a lot of microbes in your house?
DUNN: Yes, the - we have a series of interesting anecdotes that would suggest that's true. And so one of those is that there's a study from Detroit that suggests that pregnant mothers who live in houses with a dog are less likely to show evidence in their umbilical cord blood of the kinds of antibodies we associate with allergies.
It's also been shown that young children growing up with dogs are less likely to develop wheezing and asthma. And so in both cases it's been suggested that maybe what's happening is that in those houses, those children and the fetus are being exposed to more kinds of bacteria that sort of prime their immune system and make their immune system function more normally.
And so in that context I think it's interesting to speculate, we don't know this yet, that in part what we're seeing in houses with dogs is sort of this additional connection to a broader nature. And so it may be the case that as we move into more and more urban environments where we experience less and less, we experience a diversity of microbes less and less, that any of these mechanisms that connect us to more microbial species provides some health benefit.
And so there's one additional study that's pretty interesting, and it's regarded - a study in Finland. In one town in Finland, this is led by Ilkka Hanski, and this study looked at adolescents in houses that differed in which plant species they had in their backyard. And those adolescents who grew up in houses with more native plants in their back yard had different microbes on their skin and were at a much reduced risk of allergy.
LICHTMAN: It sounds - go ahead.
DUNN: No please, Flora, go ahead.
LICHTMAN: I'm just wondering, it seems like we're at the early stages still, that we're sort of in the correlations that bring up interesting questions stage but not at the causal...
DUNN: Yeah, so I think each one of these discoveries from the perspective of the scientist is very exciting, and it seems like we're on to big things that we don't know about. I think from any distance, the perspective is far more likely that we're, you know, a whole bunch of scientists leaning into this incredible darkness and with, you know, very meager lights that we're shining around and seeing cool things that we know are relevant to health and well-being, and we're trying to figure out how.
LICHTMAN: I was wondering if we should do - or if such a thing exists, that human microbe projects, like the Human Genome Project.
DUNN: Yes, there are a variety of types of human microbe projects at this point. So there are two gut projects right now that aim to characterize difference in gut microbes of people around the world. One of those in American Gut and is uBiome. And both of those projects, people can either donate or pay money to have their gut microbes sequenced.
And when they do, they can see what they have, and the scientists are going to see how that relates to what we know. And so in a way that's a beginning step. But what I think we kind of hope for is to have something akin to Mendelian genetics, where we can predict, you know, why you have a specific set of microbes and microbe genes. But we're very far from that still.
LICHTMAN: In the 30 seconds we have left, how can people get involved if they want their own microbes sampled and surveyed?
DUNN: So if you want to get involved with our projects in general, you can go to yourwildlife.org and sign up to participate. And whenever we have new projects, whether that's forehead mites or house microbes or anything else, we'll send you an email.
LICHTMAN: Thanks, Rob, appreciate it.
DUNN: Thanks so much, Flora, you have a wonderful day.
LICHTMAN: You, too. Rob Dunn is a biologist at North Carolina State University and the author of "The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today." And we should also mention that the Sloan Foundation, which Rob Dunn mentioned as a funder, also funds our sci-arts coverage on SCIENCE FRIDAY.
Stick with us. When we come back, technology for older adults.
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LICHTMAN: This is SCIENCE FRIDAY from NPR. Transcript provided by NPR, Copyright NPR.