A 2014 analysis found that New York City’s Queens was the most ethnically diverse county in the continental U.S. But when it comes to the diversity of DNA found in each borough's subway stops--the Bronx takes the prize.

"I live in Brooklyn so I was kind of hoping Brooklyn might be top of the list but we're second place. Manhattan in the middle. And then Queens, and then Staten Island." Christopher Mason, a geneticist "a very curious geneticist, I'd say" at the Weill Cornell Medical College in Manhattan.

Mason's curiosity led him and his colleagues on a five-borough tour of New York’s 468 subway stations, and the Staten Island Railway. They swabbed turnstiles, kiosks, benches, trash cans, railings and subway cars, then sequenced every bit of DNA they found. The result? "The subway kind of looks like skin." Meaning they found a whole lot of bacteria, like Pseudomonas, that also live on our skin.

The DNA at each subway stop mirrored the genetic diversity of the local residents—and, what they like to eat. "We could see other evidence of things like molecular echoes of pizza. Cucumbers, as well as chickpeas that might be from falafels or hummus." The researchers also found DNA fragments from anthrax and plague bacteria. But don’t panic. "We have zero evidence that they're alive or remotely pose a risk to public health." 

The team turned up some 1,700 organisms in total. But nearly half the DNA they sequenced could not be linked to any known organism. Assuming there’s no actual Men In Black-type extraterrestrial police agency operating underground in Manhattan, the unknown DNA means that we either haven't discovered some subway dwellers—or maybe we just haven't sequenced their DNA yet. The study is in the journal Cell Systems. [Ebrahim Afshinnekoo et al, Geospatial Resolution of Human and Bacterial Diversity with City-Scale Metagenomics]

Despite the mysterious genetic sequences, Mason says the research has made his commute a little more carefree. "And the study has replaced what used to be sort of a fog of almost fear maybe about what might be on the surface to concrete knowledge that the vast majority of everything under our fingerprints is mostly benign, so, I've become much more confident."

—Christopher Intagliata

[The above text is a transcript of this podcast.]