Mapping the Great Indoors
By PETER ANDREY SMITH
Published: May 27, 2013
BOULDER, Colo. — On a sunny Wednesday, with a faint haze hanging over
the Rockies, Noah Fierer eyed the field site from the back of his
colleague’s Ford Explorer. Two blocks east of a strip mall in Longmont,
one of the world’s last underexplored ecosystems had come into view: a
sandstone-colored ranch house, code-named Q. A pair of dogs barked in
the backyard.
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Next to You on the Subway (May 28, 2013)
Noah Fierer
A fungal spore, top, from an outer door frame and a
bacterium from an inner door frame, sampled for The Wild of Our Home
project. At each home those and seven other sites were swabbed: cutting
board, kitchen counter, refrigerator, TV screen, door handle, toilet
seat and pillowcase.
Dr. Fierer, 39, a microbiologist at the University of Colorado Boulder
and self-described “natural historian of cooties,” walked across the
front lawn and into the house, joining a team of researchers inside. One
swabbed surfaces with sterile cotton swabs. Others logged the findings
from two humming air samplers: clothing fibers, dog hair, skin flakes,
particulate matter and microbial life.
Ecologists like Dr. Fierer have begun peering into an intimate,
overlooked world that barely existed 100,000 years ago: the great
indoors. They want to know what lives in our homes with us and how we
“colonize” spaces with other species — viruses, bacteria, microbes.
Homes, they’ve found, contain identifiable ecological signatures of
their human inhabitants. Even dogs exert a significant influence on the
tiny life-forms living on our pillows and television screens. Once
ecologists have more thoroughly identified indoor species, they hope to
come up with strategies to scientifically manage homes, by eliminating
harmful taxa and fostering species beneficial to our health.
But the first step is simply to take a census of what’s already living
with us, said Dr. Fierer; only then can scientists start making sense of
their effects. “We need to know what’s out there first. If you don’t
know that, you’re wandering blind in the wilderness.”
Here’s an undeniable fact: We are an indoor species. We spend close to
90 percent of our lives in drywalled caves. Yet traditionally,
ecologists ventured outdoors to observe nature’s biodiversity, in the
Amazon jungles, the hot springs of Yellowstone or the subglacial lakes
of Antarctica. (“When you train as an ecologist, you imagine yourself
tromping around in the forest,” Dr. Fierer said. “You don’t imagine
yourself swabbing a toilet seat.”)
But as humdrum as a home might first appear, it is a veritable
wonderland. Ecology does not stop at the front door; a home to you is
also home to an incredible array of wildlife.
Besides the charismatic fauna commonly observed in North American homes —
dogs, cats, the occasional freshwater fish — ants and roaches, crickets
and carpet bugs, mites and millions upon millions of microbes,
including hundreds of multicellular species and thousands of unicellular
species, also thrive in them. The “built environment” doubles as a
complex ecosystem that evolves under the selective pressure of its
inhabitants, their behavior and the building materials. As microbial
ecologists swab DNA from our homes, they’re creating an atlas of life
much as 19th-century naturalists like Alfred Russel Wallace once logged flora and fauna on the Malay Archipelago.
Take an average kitchen. In a study published in February in the journal Environmental Microbiology, Dr. Fierer’s lab examined 82 surfaces in four Boulder kitchens.
Predictable patterns emerged. Bacterial species associated with human
skin, like Staphylococcaceae or Corynebacteriaceae, predominated.
Evidence of soil showed up on the floor, and species associated with raw
produce (Enterobacteriaceae, for example) appeared on countertops.
Microbes common in moist areas — including sphingomonads, some strains
infamous for their ability to survive in the most toxic sites — splashed
in a kind of jungle above the faucet.
A hot spot of unrivaled biodiversity was discovered on the stove exhaust
vent, probably the result of forced air and settling. The counter and
refrigerator, places seemingly as disparate as temperate and alpine
grasslands, shared a similar assemblage of microbial species — probably
less because of temperature and more a consequence of cleaning. Dr.
Fierer’s lab also found a few potential pathogens, like Campylobacter,
lurking on the cupboards. There was evidence of the bacterium on a
microwave panel, too, presumably a microbial “fingerprint” left by a
cook handling raw chicken.
If a kitchen represents a temperate forest, few of its plants would be
poison ivy. Most of the inhabitants are relatively benign. In any event,
eradicating them is neither possible nor desirable. Dr. Fierer wants to
make visible this intrinsic, if unseen, aspect of everyday life. “For a
lot of the general public, they don’t care what’s in soil,” he said.
“People care more about what’s on their pillowcase.” (Spoiler alert: The
microbes living on your pillowcase are not all that different from
those living on your toilet seat. Both surfaces come in regular contact
with exposed skin.)
Dr. Fierer has teamed up with Rob Dunn,
a biologist at North Carolina State University, to sample the microbial
wildlife in 1,400 homes across the United States. The project — known
as The Wild Life of Our Home
— relies on volunteers who swab pillowcases, cutting boards and
doorjambs, then send samples in for analysis. (Full disclosure: I am a
volunteer participant in the study, sending in swabs from my home.) Dr.
Dunn hopes that the project will begin to unravel the consequences of
moving from caves to creating environments around us in a haphazard way.
“For the entire history of humanity, we have created environments around
us, in our daily lives, in a very unintentional way. The control that
we’ve exerted is predominantly one in which we kill the ones that might
be bad,” Dr. Dunn said. “That’s saved a lot of lives. It’s also favored
this whole suite of species that we know very, very little about.”
So little is known of what’s in the home that a small sample can reveal
something new. In their first study of 40 homes around Raleigh-Durham,
N.C., published last week in the journal PLoS One, they found that humans rapidly “infect” the spaces in which they live.
We leave bacteria by touching surfaces with our exposed skin, and at
room temperature, a healthy human kicks up a “convective plume” of about
37 million bacteria per minute that disperse throughout the home and
can survive for extended periods.
Species living outdoors find their way indoors, Dr. Fierer and Dr. Dunn
found. Outdoor microbes are more frequent in homes with dogs, where
fur-associated bacteria were found adhering to TV screens and
pillowcases. “My expectation is that the effect of dogs on allergies is
similar to the effect of getting your kid playing in the dirt,” Dr. Dunn
said. “They end up being a surrogate for dirty nature in some ways, one
dirty paw at a time.”
The data from the 1,400 homes are still being analyzed, but the team
expects to learn how building materials, ventilation rates and cleaning
habits affect the microbial map. “If you’re a vegetarian, do you have
different microbes in your house than if you’re an omnivore?” Dr. Fierer
said. “If you live in a forest, do you have different microbes than if
you live in a desert? These are the types of questions that we don’t
actually know the answer to. Yet.”
The effort to catalog the creatures of the great indoors began in earnest in 2004, when Paula J. Olsiewski,
a program director at the Alfred P. Sloan Foundation in New York, sent
out a call to examine buildings as a first line of defense against
bioterrorism. “If there’s a biological threat,” she said, “you’re
probably looking for a needle in a haystack — but what’s the haystack?
What’s going on in a building?” No one knows what the natural microbial life of a building should be.
The foundation has put up $28 million for projects to date, including
continuing explorations into the microbial ecology of older two-story
homes in the Northeast, train ticket kiosks in Boston, and the opening
of a new hospital wing in Chicago. The Hospital Microbiome Project,
led by Jack Gilbert of the University of Chicago, began sampling
microbes in patients’ noses, armpits, hands and feces in February, along
with those taking up residence in the newly constructed nursing
stations and 10 patient rooms — a total of 12,000 swabs.
The yearlong investigation will tackle a pressing concern: One in every
20 patients acquires infections in a hospital, to the tune of an estimated 1.7 million infections and 60,000 deaths
annually, according to the Centers for Disease Control and Prevention.
Dr. Gilbert said, “The whole reason for doing this study is to stop
people from dying.”
His preliminary findings suggest that the longer a patient stays in a given room, the more likely it is to acquire his or her unique microbial signature.
The new hospital is being infected by its inhabitants. “You start to be
colonized by bacteria from your mother in the amniotic sac,” Dr.
Gilbert said. “If you use that as an analogue, we’re looking at the
birth of a hospital.”
Another study, published in 2012 in The ISME Journal, found that hospital patients were more likely to encounter potential pathogens in mechanically ventilated rooms
than in ones with access to fresh air from outside. Jessica L. Green,
the study’s author, a theoretical ecologist at the University of Oregon
and director of its Biology and Built Environment Center,
said she expected buildings to eventually be redesigned with a view
toward managing their microbial impact on human health.
Architects and engineers also could try to cultivate benign or
beneficial species, favoring certain conditions and altering our
chronic, long-term exposure. One 2012 study in Finland,
for example, found that plant diversity outside was linked to a greater
variety of bacteria on human skin inside homes; moreover, teenagers
with this increased biodiversity were at lower risk for allergies.
We are outliers among species, like leaf-cutter ants or termites, that
garden beneficial organisms for their own benefit. “We keep beautiful
forests far, far away. Crops that we can eat are far, far away,” Dr.
Dunn said, adding that our cities are full of waste treatment plants.
“An ant would never do that.”
The future of indoor ecology, now in its infancy, hinges on answering
questions about what we should intentionally surround ourselves with.
“Right now, we don’t understand how buildings work” as ecosystems, said Jordan Peccia, an environmental engineer at Yale.
Dr. Peccia is examining the link between increased fungal diversity
indoors and reduced rates of asthma. Someday, he said, managing indoor
biodiversity will run up against traditional concerns about building
cost and energy efficiency.
“We’ve seen it as an improvement to make homes more insulated, but maybe
that’s a mistake from the standpoint of ecological diversity,” he said.
“We’re far from making a quantitative analysis of the trade-off. And
once it’s shown, it’s another huge step to convince architects and
engineers that this is important enough.”
We do not have a choice about whether to share our homes with microbes,
then, but soon we may have an opportunity to open them up to better
company.
Back in Colorado, Dr. Fierer talked with Amanda Phillips, 61, who lives
at Home Q with her husband, Chester, 67, and their dogs Hunter and
Chase. Ms. Phillips admitted she did some extra cleaning before the
team’s arrival.
As she got up to leave, she said she was wary about the effort. “I don’t
know if I really want to know what you’re finding,” she said. “But I’m
excited to learn.”
