Remember this when the world becomes lonely: we’re all marinating in a communal cauldron of microbial life. For the most critical part, this is a positive thing. You may have heard of the human gut microbiome, a community of microscopic organisms in our digestive system that might impact our health in still-unknown ways. Still, cities, too, have microbiomes—and new research reveals that they’re all different, with compositions that vary from city to city.
The study was published in journal Cell on May 26th, mapped out microbial communities in 60 cities across six continents, evaluating over 4,700 samples collected from subways and bus networks to determine the bacteria, viruses, and archaea that reside there. Lead author Chris Mason, an assistant professor at Weill Cornell Medicine in New York, adds, “What we knew previously is that there were undoubtedly hundreds of species awaiting us at every turnstile and bench.” “However, we had no idea how diverse these microbiomes are in various cities.”
Over three years, a multinational team of researchers swabbed ticket kiosks, railings, seats, turnstiles, and other heavily-touched surfaces in public transport systems worldwide, including Bogotá, New York City, Tokyo. Cutibacterium acnes, a common bacterial species that grow on human skin, was among the 31 “core” species discovered in virtually all locations, according to the researchers. However, they found that microbial communities in various cities had varied makeup, or “signatures.”
According to Mason, these discrepancies might be attributed to diverse surroundings with varying temperatures and humidity levels. They also discovered varying quantities of genes that signify possible antimicrobial resistance—a worldwide health concern—across cities, which the researchers believe may represent the antibiotics used locally. The good news, according to Mason, is that in the metropolitan environment, fewer genes are indicating antimicrobial resistance than in soil or human gut samples. The researchers also discovered a large amount of previously unclassified DNA from viruses and bacteria.
“Every time you sit down [on the train], you’re probably sitting right on top of an undiscovered species,” Mason adds.
In an email to Popular Science, Maria Gloria Dominguez-Bello, a professor of microbiology at Rutgers University who wasn’t involved in research, said, “This work gives the first systematic review of built environment genes globally.” It’s significant because it provides new knowledge about our contemporary environment, which is substantially different from the one in which our forefathers originated, she writes.
“Traditionally, when we think about microorganisms, the environment, and health, we’ve concentrated on pathogens and trying to sterilize surfaces as much as possible,” commented Erica Hartmann, an assistant professor of civil and environmental engineering at Northwestern University. She was not involved in the study. During the current COVID-19 outbreak, this was especially true. “By taking the step back and looking at all microbes and seeing what’s there, it gives us a different perspective, one that will hopefully lead to better approaches to managing our microbial cohabitants”—such as noting which microbes are present normally and reassessing when and which disinfectants are needed.
“Microbes are everywhere around us, and while some can make you sick, the great majority are neutral or even beneficial,” Hartmann continued. “It’s critical to work with microorganisms rather than against them so that we don’t create new issues, such as superbugs.”
With over half of world’s population living in cities, Mason believes that city services such as public transport are “perhaps the largest common tactile ecology that we all have.” He claims that knowing what’s in this ecosystem can help us figure out how to keep urban microbiomes robust, diversified, and pathogen-resistant.