A glorious picture of the true-life story inside the New York City subway system is now a little more complete with the identification of DNA fragments swabbed from such system surfaces as benches, poles and turnstiles. Researchers identified nearly 1,700 species of bacteria, viruses and eukaryotes to create a “metagenomic” map of the city. One cluster of points on this grid offered a reminder of exactly how inundated and overwhelmed the city was more than two years ago when Superstorm Sandy hit.



Nearly half of the mapped DNA came from as-yet undocumented organisms, highlighting how much remains unknown to science about the microbial world around us. The results are detailed in the February 5 Cell Systems. The study's senior investigator Christopher Mason, assistant professor in computational biomedicine at Weill Cornell Medical College, says the findings are "akin to standing in front of a rainforest and standing in awe of the amount of diversity available there."



The most commonly identified DNA in the sample came from bacteria. And although strains of the causative agents of anthrax and bubonic plague surfaced, the vast majority of species identified were harmless. No cases of either disease have been reported in the Big Apple in the past few years, suggesting that these species are somehow a part of its natural urban environment. Mason says these dangerous DNA snippets occurred only at trace levels, so they could have been fragments that other bacteria picked up through horizontal gene transfer or even have come from dead organisms. Most of the bacteria identified are types that placidly thrive on our skin and are of no concern to Mason. "If anything, I've become much more confident riding the subway," he says.



But researchers found one of the stations was not like the others. The South Ferry station in Lower Manhattan had the most unique profile of bacteria in the system, and still resembled a marine environment. When the storm surge from Hurricane Sandy hit the city in 2012, the station filled with about 57 million liters of water that rose to 25 meters deep. The Metropolitan Transit Authority estimated at the time that rebuilding the station would cost $600 million and take three years. Part of the high price tag derived from the fact that saltwater damaged nearly all of the station’s electronics.

Yet with the destructive seawater came life. The researchers isolated 10 bacterial species that were only found at South Ferry. Among these were Shewanella frigidimarina, which has been found in the North Sea, and Flavobacterium, which can harm certain species of fish. The unique bacteria are usually found in cold, marine environments, so the researchers wondered if Sandy's storm water dragged them in.



A total of 12 sites were also sampled in the Gowanus Canal, the inlet of water in between Red Hook and Park Slope in Brooklyn that experienced intense storm surge after the storm hit. There was a little bit of overlap among species found in the Canal and those back at the station in Manhattan, but 10 species were only found in at South Ferry, indicating they truly traveled with the surge from Hurricane Sandy.



Mason says the microbiology of highly trafficked areas at South Ferry will likely resemble that of the system’s other stations once it reopens but less-accessed areas such as the tracks could retain their enchanting marine signature for a long time. As climate change intensifies, New York will likely see stronger storm surges due to sea level rise and the slow sinking of Manhattan itself. How the possible future intermingling of aquatic and land communities could affect one another or humans has yet to be seen.