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If you were seeking a seething mass of microbes, it'd be hard to think of a better place to look than the New York City subway system.

Scientists who descended into that subterranean maze in search of its microbial tenants wanted to find out how the 5.5 million people who use the system each weekday influence the microbes, and vice versa.

But the 18-month-long project, which sampled DNA from 466 stations, was no walk in Central Park.

As Robert Lee Hotz of The Wall Street Journal reports:

"[S]cientists and student volunteers gamely dodged rats and gingerly worked around discarded pregnancy tests, used condoms, puddles of vomit and rotting food to swab surfaces in every subway station. On more than one occasion, suspicious police stopped them and escorted them to the street."

The intrepid explorers discovered that the city's microscopic inhabitants are just as diverse as its human denizens.

  • Almost half of the microbes, 48 percent, are previously unknown.
  • Stations in the Bronx had the widest range of microbes, while those in Staten Island held the lowest diversity.
  • Most of the bugs found were harmless, but 12 percent of the bacteria could be associated with disease, including the one that causes bubonic plague (carried by rats, natch). But the bad bugs are normal, the researchers said, and there aren't enough of them to sicken passengers.
  • Human DNA sometimes reflected the residents of the neighborhood, with more Asian and Hispanic DNA found near Chinatown, for instance.
  • Each subway stop has its own genetic fingerprint. A stop in Bedford-Stuyvesant, Brooklyn, had the most diversity, while the closed South Ferry Station, which flooded during Superstorm Sandy, had the strangest microbiota, looking more like a cold ocean.

The project, which was led by researchers at Weill Cornell Medical College, is just one of many efforts around the world trying to map human environments, indoors and out. The study was published online in the journal Cell Systems on Thursday.

The subway microbiome could perhaps be used to monitor trends in human disease, the researchers speculate, detect bioterrorism weapons or even solve crimes.

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