IRA FLATOW: This is Science Friday. I’m Ira Flatow. We talk a lot about the microbiome of our gut and the trillions of bacteria, viruses, fungi living inside of us that may influence our health and happiness. At the same time, there’s a world of microbes outside our bodies that we’re perhaps less familiar with, even though they sleep with us, they shower with us, they eat with us, they live with us in our offices and homes, the microbiomes of where we live and work.

These organisms thrive indoors, despite our best efforts to keep them out. And they can affect our health in ways scientists aren’t yet clear about. So recently, the National Academies of Sciences, Engineering, and Mathematics published a report that included questions researchers still want answers to, including which microbial community should we treat as unwanted guests, and which do we welcome in with open arms, literally? And how do we build living spaces that promote a healthy indoor microbiome?

Joining me to discuss these questions are my guests, Jessica Green, professor of biology at Oregon State University and CTO of Phylagen. Welcome to Science Friday.

JESSICA GREEN: Thank you. I’m delighted to be here.

IRA FLATOW: Nice to have you. Rob Dunn, professor of applied ecology at North Carolina State University and author of The Wildlife of Our Bodies. He joins us by Skype. Welcome to Science Friday.

ROB DUNN: Oh, it’s great to be on. Thanks, Ira.

IRA FLATOW: You’re welcome. Rob, this idea that there are microbes in your home, it’s really not surprising to anyone. But we don’t like to think about it. I know if we were looking to go where– where should we find some of these communities in our homes?

ROB DUNN: Well, I mean, sort of everywhere. I mean, they’re divided up. And so every place you lie down or sit down or go to the bathroom or eat something, there’s kind of an aura of you. But then if you look around in more detail, there are these smaller habitats that have specialized microbes, like in your sourdough bread, in your beer, or in your cheese. And so it’s a very complex ecosystem around you right now.

IRA FLATOW: Are any of them in our homes particularly harmful, that we bump into every day?

ROB DUNN: Sure, there are definitely species and be harmful, far fewer than there would have been in your home in 1800 in London, say. But I think what’s more conspicuous than the harmful species that are present is so many species that we used to be exposed to in her home that are now missing. And so in a way, the homes we’ve created today, they aren’t marked so much by what what’s there as by what’s absent in a lot of ways.

IRA FLATOW: Dr. Green, forgive me for saying Oregon State University. I know it’s University of Oregon. And I will get whipped for that late on.

JESSICA GREEN: Not a problem.

IRA FLATOW: Let me ask you about the researchers. A bunch of them got together to author this report. What conclusions did they come to about the indoor microbiome?

JESSICA GREEN: Well, it was a fantastic group. It was a pleasure to serve on the committee. And the committee decided that the agenda for the future was to really develop a microbiome-informed built environment that both considered occupant health and energy efficiency. And the committee outlined the what, the why, and the how of how to make that happen.

IRA FLATOW: I was watching a Ted Talk you gave describing how a building– you picked out a building and showed that in this office space there could be all different kinds of microbiomes, depending on where the office was located, where the air ducts were, I guess the point being there’s not just one microbiome in any place.

JESSICA GREEN: Absolutely. So what’s incredible is that engineers and architects, without realizing it– and even ordinary people in the home, without realizing it– through our behavior, we impact these microbial ecosystems that Rob referred to. And we’re just beginning to understand how we can manage indoor ecosystems. And what the committee identified was a key component of this is being able to measure what we’re exposed to in the indoor environment and these complex ecosystems.

IRA FLATOW: And Rob, that’s what you do. You measure what’s living in our homes.

ROB DUNN: Yes. We’ve spent a lot of time sort of doing the Alexander von Humboldt approach to exploring houses, and so really trying to figure out what’s in houses. And so we surveyed the dust in 1,000 houses across North America, and now with Noah Fierer we’re working on showerheads and sourdough bread. And as Jessica points out, there’s tons to understand. And so part of what needs done now is just to figure out what’s there in the first place. And it makes it very, very fun from an exploration perspective.

It’s also daunting, because we realize that, as we explore what’s in homes, these species also have health and well-being consequences. And so– fun because every corner yields some totally new discovery, disappointing because we can’t always say what that means for what you should do next.

IRA FLATOW: I was on your web site, and I saw that you had a project about showerheads. And tell us about– when you take a shower, you’re not showering alone, are you?

ROB DUNN: Well, yeah. So the showerhead’s full of these crazy little biofilms, which are like a house that the microbes build for themselves [? and ?] others. And in those biofilms, we know that sometimes there are species that can cause problems, especially if you’re immunocompromised, which lots of people are now. But then also species that look like they’re probably beneficial, that they’re triggering positive immune responses in you.

And so what’s falling on you, into your eyes, into your mouth, it’s almost definitely affecting you in some way. But we don’t have a very good understanding of what determines which [AUDIO OUT] are in your– what showerhead versus your neighbor’s showerhead versus the hotel showerhead. And so we have a survey around the world with Noah Fierer to try to figure out what’s in there, what it’s doing.

IRA FLATOW: I understand you also think that the kitchen’s dishwasher is an interesting place to put it, euphemistically.

ROB DUNN: Yeah. That’s not our work, but people have shown in the soap dish in the dishwasher, there’s a pretty gnarly fungus. And it seems to really like conditions that are dry and then wet and then soapy and then not soapy. But it’s also very unusual, because we know it’s present in dishwashers. And then it’s also present in the feces of tropical fruit bats.

And I think that’s sort of indicative of where we are in understanding. Because clearly, there’s some connection between those two. We just don’t– we haven’t sampled where else it might live or what else it’s doing. But the cool part about that is a lot of these species we find in weird habitats in houses, they can be really useful, still. And so think about your bread mold that yields antibiotics.

We work on camel crickets in people’s basements, and we found new bacteria that can burn industrial waste into energy from those. And so on the one hand, well, I wish that I knew what was going on with that thing in the dishwasher. On the other hand, once we find it, we can make use of it, too.

IRA FLATOW: Jessica, I can imagine that we’ve heard about the microbes running around in hospitals. We don’t want certain microbes infecting our patients. But how much do we want a completely sterile environment? Where is the trade-off? What is the perfect situation?

JESSICA GREEN: That’s a great question. I just ran into Bill Nazaroff here on the Cal Campus, UC Berkeley. When I took classes from him about two decades ago on indoor air quality, the thesis was that you want to keep microbes out of the indoor environment and that microbes were pollutants. But we now really understand that, just like Rob said, there are good actors and bad actors in the indoor environment. And what we want to do is, again, manage the indoor environment so that we increase exposure to the good actors.

IRA FLATOW: And how do you manage it?

JESSICA GREEN: Well, there’s lots of different ways to carry out interventions in the indoor environment. You can manage the way you ventilate or your filtration system in the indoor environment through cleaning, temperature and relative humidity, through your behavior. Or there’s even some new research findings showing that the way that you manage vegetation outside of your home and landscape architecture might impact the microbes that you’re exposed to inside the home.

IRA FLATOW: So architects are thinking about that stuff now when they design buildings?

JESSICA GREEN: They are. I mean, it’s very forward-leaning architects. But my colleagues at the Biology and Built Environment Center at the University of Oregon are really paving the way of this group of architects and engineers and microbiologists that are working together. And there’s many other groups around the world that are thinking this way now.

IRA FLATOW: Rob, how about when we build a building now? We’ve designed it, and we want to build it. We start construction. Does this construction itself bring some nasty things indoors that you don’t want there?

ROB DUNN: Yeah, there’s just some really neat, recent– neat’s the wrong word, because it’s that horrible [INAUDIBLE]. There’s some interesting recent research showing that one of these sponges we worry about when houses get wet, is toxic black mold that Birgitte Andersen at the Danish Technical University has shown that if you buy a brand new drywall, that that mold is actually already in the drywall in many cases. And it’s just hanging out there, quiescent. And then when the drywall gets wet, it sort of happily grows through it, like some monster out of a kids’ book.

And Jessica made this point well. We make all these decisions about how we build houses, pretty oblivious to how each one of those decisions moves species in and out. And I think one of the great ironies of all of this is that in many cases, the healthiest thing you can do in terms of your built environment is basically to make it more like the outside. You know, you open the windows. You increase flow. If the outside’s polluted, that’s no longer the case.

But so in many ways, the last years of really sealing up houses tighter and tighter, trying to kill everything, keep it clean, it took us pretty far down the wrong road. And so we’re having to pause and think about where we are. Do we need to backtrack? Do we need to totally revisit what’s going on here? And so there’s kind of a moment of reckoning.

IRA FLATOW: So Jessica, when I go into a musty, old room that has not been– the windows have been closed for a while, and people have used it before. I’m actually walking into their microbiome because there hasn’t been any circulation.

JESSICA GREEN: It is true. Research has shown that humans and the human microbial cloud has a great impact on the indoor microbiome. We don’t know the degree to which you pick up microbes from what people have left behind. But when a person is in a room every hour, just through directly shedding their microbes or resuspending microbes in that space, they contribute more bacteria, just bacteria, per hour than the number of people that live in the state of California.

IRA FLATOW: Wow. I’m Ira Flatow. This is Science Friday from PRI, Public Radio International. Talking with Rob Dunn and Jessica Green about the microbiome. So if I’m moving in– now, let’s say I’m moving from my home into someone else’s home. Someone has been living there with a family and dogs and whatever for a while. How long does it take for the microbiome to turn over, and could I possibly be having a reaction to the microbes that they left behind? Rob, any–

ROB DUNN: Oh, yeah, it’s a super good question. We don’t have a great answer to that. I mean, in some way, when you first move into the house, for sure, you’re being exposed to a whole suite of what was there before. And some of it’s kind of that cloud of the last person. Some of it is– the salt shaker has salt-adapted microbes. The showerhead has its microbes. And each of those is sort of going to be changing at a different rate.

I think the way we often think about that is that it’s kind of gross. But there’s also something beautiful inasmuch as we’re part microbial, a great part microbial. And so it’s this kind of sharing with the ghosts of inhabitants past. And we do it all the time.

So if you think about when we make a sourdough bread. That sourdough bread includes microbes that are colonized out of the air and from your hands. And so that bread has some of that. It embodies everybody who’s in that room. I think there’s a kind of beautiful element to it in addition to the [INAUDIBLE] version that probably we most worry about. But the short answer is we don’t know.

IRA FLATOW: Yeah. And sure, we are living even with the soil microbiome, too. That’s coming in and out of the house. And so this is like a hot topic. This is where a lot of cutting-edge research is, isn’t it?

ROB DUNN: We both hope so, yeah.

JESSICA GREEN: Yeah.

ROB DUNN: [INAUDIBLE]

IRA FLATOW: OK, well, as our listeners know, this is one of our favorite subjects. We’ve been talking about this for probably almost 10 years now. We’re bringing everybody along with us. I want to thank both of you for taking time to be with us today. Jessica Green, professor of biology at the University of Oregon and Rob Dunn, professor of applied ecology at North Carolina State University and author of The Wildlife of Our Bodies. Thanks for taking time to be with us today.

ROB DUNN: What a great pleasure.

JESSICA GREEN: Thank you.

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