Why you should care
Because where we live might affect our health by shaping the germs that live inside us.
By which we mean your home. The walls, the counters and even the showerhead teem with fungi, yeast, bacteria and other single-celled microorganisms — or what scientists call, collectively, “microbes.” Never mind your OCD cleaning: Your very skin sloughs off millions of microbes an hour as you wander, innocently, from room to room. This might sound gross, but some microbes are very, very good for you.
A growing community of scientists is investigating the microbial ecosystems, or microbiomes, that dwell in homes, offices, hospitals and other man-made structures. They’ve started by cataloging these microbes to understand how different aspects of building design, from lighting to ventilation, can influence the microbiome. Some researchers are unraveling possible links to disease. That might mean designing buildings to promote healthy microbiomes — or even seeding them with living microbes. One day, architects might consider these organisms as much a part of the building blueprint as construction materials and HVAC systems.
Thanks largely to next-generation DNA sequencing, which allows researchers to identify microbes more quickly and cheaply than ever before, interest in the field has grown at a staggering pace. A Google Scholar search of “microbiome” and “built environment” turns up about a dozen papers published in 2010. Since then, that number has swelled to more than 600. The Alfred P. Sloan Foundation’s Microbiology of the Built Environment Program has awarded more than $43 million in research grants since 2004. And the EPA recently charged the National Academy of Sciences with conducting a study on indoor microbiology.
We know nothing about the ecology of the microbes in buildings … despite spending an estimated 90 percent of our lives indoors.
It’s all part of the evidence-based design movement, which uses research to inform design that promotes health and well-being. Now, biologists and building scientists wonder whether they should also consider the recent groundswell of microbiome research — including, at times, embracing microbes. “It’s this paradigm shift [from the notion] that all the microbes in the building are bad and sealing them off,” says Gwynne Mhuireach, a graduate research fellow at the University of Oregon’s Energy Studies in Buildings Laboratory. The shift stems partly from studies suggesting that exposure to microbes early in life helps “train” the immune system, lowering allergy risk, and that disturbances in the gut microbiome could be linked to asthma, depression and other health problems. More broadly, understanding the microbiology of the built environment could help address mounting concerns about antibiotic resistance and help us design healthier cities for growing urban populations.
Many researchers have begun simply with documentation. “We know nothing about the ecology of the microbes in buildings,” says Jonathan Eisen, principal investigator of the Built Environment Network (microBEnet) — even though Americans spend about 90 percent of their lives indoors. So far, studies have found that microbiomes can vary widely even within a building. University of Oregon researchers reported in PLOS ONE that human traffic, building arrangement, space type and ventilation play a major role in shaping the microbiomes in an on-campus building. The microbiomes of restrooms differed drastically from those in other rooms. Spaces ventilated with windows contained microbiomes that resembled those found outdoors, while HVAC-ventilated spaces looked more like those in the human gut and saliva. Researchers have begun to examine how sunlight affects the microbial communities on dust particles. (Most glass in buildings excludes the majority of UV light.)
Some are already exploring health implications. Christopher Lowry’s lab at the University of Colorado Boulder, for instance, is investigating the effects of microbes on mental health. Inflammation and urban living have surfaced as major risk factors for psychiatric disorders — could indoor microbes trigger the inflammation associated with mental illness? To find out, Lowry plans to measure stress outcomes of mice after exposing them to a type of soil bacteria that he’s shown to have antidepressant-like effects.
Meanwhile, Jordan Peccia of the Yale School of Engineering & Applied Science led a study comparing fungal and bacterial communities in dust from the homes of children with allergic or nonallergic asthma. Among those with allergic asthma, the amount of fungi in the dust didn’t matter as much as the dust’s composition — the more allergenic species in the dust, the more severe their asthma. But among kids with nonallergic asthma, the more fungi — regardless of the type — the worse their symptoms. People often track in fungi from their shoes, Peccia says. Some flooring materials might be more likely to waft microbes into the air, but “we don’t have a great handle on what they are. It seems like carpeting is the worst, and hard flooring is better.”
Studies have hinted that the microbiomes in the homes of people with asthma might even play a role in the disease’s development. In 2013, University of California, San Francisco researchers found that mice exposed to dust from a household with a dog had reduced asthma-like symptoms when exposed to cockroach and egg-protein allergens. In a similar study published in The New England Journal of Medicine this August, another team compared dust in Amish and Hutterite homes. Despite their common genetic origins, Amish children have a lower risk of allergies. Sure enough, mice exposed to dust from Amish households were protected from asthma-like symptoms, while dust from Hutterite homes triggered them — possibly because the Amish live in closer proximity to their livestock, resulting in dust with a richer array of microbes.
The findings hint at an alluring prospect, that we might be able to design buildings that foster healthy microbiomes, or even prevent disease. An alternative approach would involve adding microbes directly to buildings. (Eisen says that several startups have already contacted him about the possibility.) But scientists have many more questions to answer before we begin pursuing proposed solutions. The problem is, “we still don’t know what the target is,” says Noah Fierer, a biologist at CU Boulder. “We don’t know what a good microbial community is.”
For now, scientists continue to forge ahead with basic research. Eisen, for instance, is making the foray into other built environments, including zoos, aquariums — and even the International Space Station. “It’s an exciting time,” Fierer says.