University of Oregon researchers Jessica Green and G Z 'Charlie' Brown call it the Pickle Box. This former walk-in storage unit for pickles, remodelled into an enclosed climate chamber, is helping scientists understand how people shed their own 'microbial cloud' in a built environment.

The bacteria, fungi and other microbes that we leave behind in indoor spaces – a kind of calling card – may help determine the character of a building's entire microbial community, or its microbiome.

"We're finding that individuals have quite a strong and unique microbial cloud, and so every person that's inside is contributing their microbiome to the built environment," says Green, Director of the university's Biology and the Built Environment Center. From other studies, the same seems to be true of pets.

Most research on how a building's design and operation may affect its indoor environmental quality has been based on physics or chemistry, Green says. With advanced DNA sequencing technology and an explosion of information about what researchers are calling 'invisible ecosystems' within buildings, however, researchers are beginning to focus on the microscopic menagerie inhabiting structures such as offices, hospitals and portable classrooms. Astronauts are even tracking the microbiome within the International Space Station.

We already know that improper design, use or maintenance of a building can harm human health – Legionnaire's disease can spread through water systems while serious infections like methicillin-resistant Staphylococcus aureus can spread through hospitals. Rather than focus on a specific pathogen or allergen, however, Green and other scientists hope to gain a more comprehensive view of risks and benefits by surveying entire microbial communities and their environments.

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In a study of a Portland hospital, for example, Green and colleagues found that window-ventilated rooms had much more diverse airborne bacteria than mechanically ventilated rooms. In the spaces ventilated via windows, the microbes' gene sequences aligned more closely with those found on plant leaves and in soils. In the mechanically ventilated rooms, the gene sequences aligned with human-dwelling microbes found on the skin and in the mouth.

In a separate study of a university building that uses a ventilation system called a 'night flush' to efficiently heat and cool the space and replenish the air, Green and Brown found that the system also flushed out many of the microbes shed from human occupants during the day. "So that human signal washes away," Green says. The results suggest an intriguing application of building microbiome analysis: using changes in the microbial signature to assess how well an indoor space is ventilated. More broadly, Green sees a future in which biosensors quickly measure the air quality of an indoor space through the composite traits of its microbiome.

Among the research efforts elsewhere, a team from the University of Texas recently secured funding to examine the microbiomes of portable classrooms in the hot and humid air typical of the southern and south-eastern USA. In particular, they plan to study how differences in air pressure and airflow patterns within the portables – which can change as the structures age – influence the types of microbes found in the classroom spaces.

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Air might be drawn in through a crawlspace, an attic or the walls, for example, changing the mix of bacteria swirling around in the indoor environment. If the researchers can understand how these factors influence the microbiome within typical portable classrooms, they might be able to draw comparisons with next-generation portables designed with improved ventilation in mind.

Researchers are also tracking the microbiomes of ultra-green buildings, like the nearly self-sufficient Bullitt Center in Seattle, to see whether their microscopic inhabitants are fundamentally different from those in other structures. "This building is so unique, and it was an opportunity to see it from the point of occupancy out, so we could kind of see how the bugs develop over time," says Scott Meschke, Associate Professor of Environmental and Occupational Health Sciences at the University of Washington.

If scientists can better understand these microbial tenants, Green says, they can begin exploring the impacts on a building's human occupants. "Given that we spend 90 per cent of our lives indoors, it's a very reasonable hypothesis that we get a lot of our microbes from the built environment," she says. "That begs the question: Can we design and operate the buildings that we live, work and play in to have an optimal indoor microbiome that's conducive to health?"

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This article first appeared on Mosaic and is republished here under Creative Commons license. Image by Khaled under Creative Commons license.