Every City Has a Unique Microbial “Fingerprint”

From architecture to microbes, every city is different

Johannes Mann/Corbis

Every city is different, from their architecture to their residents. But as it turns out, scientists have discovered a whole new element that makes every city unique: their microbes.

Over the last few years, researchers have begun realizing just how large a role microbes play in everyday life. Known collectively as the “microbiome,” these communities of bacteria, fungi and viruses can have a significant impact on people’s long-term health, affecting things like appetite and allergies. Even different rooms and buildings can have their own individual microbiomes. Now, according to a study published in the journal mSystems, researchers have found evidence that suggests cities have their own unique microbial “fingerprints.”

In the study, researchers collected samples from nine offices in three different cities over a year. While the cities were scattered all across North America (the scientists chose locations in Flagstaff, Arizona, San Diego, and Toronto), each office was rigged so the researchers could monitor their internal environments, Louise Matsakis reports for Motherboard. Though each city has a distinct climate, sensors installed inside the rooms let researchers monitor the temperature, humidity and even how much light each office got.

According to the study, bacteria typically found on human skin made up 25 to 30 percent of all microbes in the offices. However, the most common bacteria the researchers found were species that also live outdoors, suggesting that they hitched a ride into the offices, Katherine Du reports for NPR.

"We suspect that in the absence of extreme conditions like flooding, microbes may be passively accumulating on surfaces in the built environment rather than undergoing an active process," study author Gregory Caporaso said in a statement.

After a year, Caporaso and his colleagues discovered something else remarkable: each city had its own unique microbial “fingerprint.” Samples taken from offices in the same city were similar enough to each other (and different enough from those in other cities) that they could identify which city an unidentified sample came from 85 percent of the time, Matsakis reports. That’s a big surprise, considering how different individual people’s microbiomes are from each other.

“If you look at a human microbiome, say two skin samples from two different individuals or a skin and gut from one individual, those differences are going to seem massive in comparison to what this study showed,” study author John Chase tells Christina Procopiou for Newsweek.

The researchers hope that learning how microbes collect and thrive in built environments might lead to a better understanding of how cities might affect people’s health, but it has other applications as well. Samples of a person’s microbiome might one day give hints as to where in the world they have lived or traveled, even without records like a passport, Matsakis reports. A place’s microbiome might even be able to tell scientists something about its history by studying what kinds of microscopic critters thrive in different places.

“Those of us who study the built environment want to get to a point where we can say: Here is what a normal range of microbial activity for a healthy built environment looks like, and here’s what it doesn’t look like,” Chase tells Procopiou. "Is there a microbial community in the built environment that will harbor pathogens and is there not? Knowing that cities have distinct microbial communities will be part of getting to that point.”

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