Cities Have Unique Bacterial Fingerprints
Human skin is the largest identifiable source of the bacterial samples, making up 25 to 30 percent of the microbiomes. Continue reading →
Used to be you knew which city you were in from the food, the sports team, the historic sites, even the local brew.
Now a team of microbiologists discovered they can tell cities apart by their unique bacterial fingerprints.
The surprising finding was made after an intense study led by John Chase of Northern Arizona University's Department of Biological Sciences and Center for Microbial Genetics and Genomics. He and his colleagues spent a year swabbing for samples at nine offices in San Diego, Flagstaff, and Toronto.
They wanted to find out what kind of impact factors like geography, location in a room, seasons, and human interaction have on the microbial communities we spread around, called microbiomes. The researchers wanted to study microbiomes in the built environment, meaning bacteria around offices. Yeah. I can only imagine.
Their strategy involved installing the same carpeting, ceiling tiles, and drywall swatches in the various city offices to compare bacteria. In addition to swabbing those materials, they collected skin, nasal, oral, and fecal microbiome samples from office workers and the researchers doing the sampling. Science!
First, their results showed that bacterial communities don't actually differ by the material in an office, but they do vary by location within an office. "Floor samples were significantly richer than either ceiling or wall samples," the researchers wrote in their findings. In other words, the floor is really grody. Don't sleep there.
Another conclusion was that human skin was the largest identifiable source of the samples, making up 25 to 30 percent of the microbiomes. The biggest finding, though, was that regardless of factors like season or office location, the microbiomes are city-specific.
In order to test their results, the team created a computer model that used machine learning to guess which city a particular sample came from based entirely on the microbes. Amazingly, their model, called a support vector machine, predicted the city of origin with 85 percent accuracy.
The team's results were published this week as an editor's pick in the microbiology journal mSystems. "...we find that offices have city-specific bacterial communities, such that we can accurately predict which city an office microbiome sample is derived from," the scientists concluded.
Spring cleaning is a creepy reminder that dust is full of dead skin, and I try very, very hard not to think about that. So it's not entirely surprising that a bunch of people working together in an office would contribute to a unique microbial community.
What's truly weird to me is that these are a city-specific communities rather than office-specific ones. I guess that once a city gets under your skin, it's hard to simply brush it off.
Images from satellites and spacecraft can provide big-picture perspective, as it were, on how cities develop and grow. Above is Earth's most populous city, Shanghai, as seen at night from the International Space Station. For more images and galleries, check out NASA's sprawling
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Photographed in February, 2014, this image of Green Bay, Wisc., shows the city in typical winter conditions, with the bay itself icebound and covered in snow. The open water at the mouth of the Fox River indicates the location of warm water emissions from the nearby electrical power station.
The chaotic sprawl of London shows how the city was built up gradually, starting in the first century A.D., around the bends of the River Themes. The many parks and green spaces are a testament to modern urban design -- Londoners can walk for miles through the city on grass and trails.
This close-up of the island of Manhattan, in New York City, shows the city's orderly grid layout of streets and avenues. The city's rigid grid plan -- established by lawmakers in 1811 -- was initially controversial, but has since been recognized as visionary by scholars and urban planners.
China's capital city, Beijing, is one of the world's oldest and most densely populated cities. The false-color images above -- using green, red and near-infrared bands -- show the cityscape effects of the massive population growth between 1978 and 2011. Unofficial estimates put the current population of Beijing at 21 to 22 million.
The waterfront city of Sydney, Australia, is home to more than 4 million people. Apart from its shoreline, Sydney is surrounded on all sides by national parks and preserves, resulting in dense urban development. The strips of land extended into Botany Bay, at the bottom of the image, are runways for Sydney Airport.
The second-largest city in the world by population, Karachi is home to an estimated 23.5 million people. The central portion of the city is the oldest district, with winding narrow streets typical of ancient settlements in the region. The outer grid plan areas of the city were largely developed in the 19th century.
The transcontinental city of Istanbul straddles Europe and Asia across the Bosphorus Strait. In this false-color image from 2011, urban areas are shaded in gray with plant-covered areas in red. Istanbul's urban sprawl has largely taken place in the last 50 years, with population jumping from around 3 million to more than 14 million.
This composite image of Earth's city lights at night, compiled from satellite imagery, shows how cities tend to grow along coastlines and transportation networks, like highways and rail lines. The line of lights crossing central Asia follows the path of the Trans-Siberian railroad.