Probing the Aerosol Microbiome of New York City’s Subway System

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River of "psychomagnotheric slime" in the NY subway from the Ghostbusters game for Wii.

River of “psychomagnotheric slime” in the NY subway from the Ghostbusters game for Wii.

If you’re a sci fi geek like me, you’ve almost certainly consumed some form of media that features perilous encounters in the New York City subway system (our AI oppressors in The Matrix, giant genetically engineered cockroaches in Mimic, negatively charged slime in Ghostbusters, lots and lots of villains in Teenage Mutant Ninja Turtles….I could go on). In reality, any non-human dangers that do exist in the subway are likely to be more insidious than the large, charismatic monsters featured by Hollywood. Do the microorganisms inhabiting subterranean bowels of New York pose any real threat? If a dangerous epidemic were to hit the metropolis, would it spread above ground or propagate below?

While zombie viruses may be a bit far-fetched, the possibility of a pathogen propagating through heavily-trafficked subway is not

While zombie viruses may be a bit far-fetched, the possibility of a pathogen propagating through the heavily-trafficked subway is not

Motivated by these sorts of public-health questions, a team of medical microbiologists led by Dr. Norman Pace at the University of Colorado, Boulder, decided to investigate the airborne microorganisms inhabiting the NYC subway. Historically, the regulatory focus on city air quality has addressed particulate materials (soot) and chemicals.  Comparably little attention is paid to the airborne microbes and other biomaterials to which we are regularly exposed. However, in heavily-trafficked public locations like the subway (with a ridership exceeding 1.5 billion per year!), airborne pathogens may represent a much greater danger than chemical pollutants.

For  nearly two years, Dr Pace and his team collected “bioaerosols” on seven NYC subway platforms and three neighboring above-ground sites, using a device known as a fluid impinger- essentially a fancy vacuum that sucks up and filters air, trapping bacteria-sized particles. They used a combination of molecular techniques to determine the genetic composition of subway bacterial communities.

Their diagnosis? Breathe easy! There appears to be no imminent danger posed by subway air. The subway microbiome is relatively simple and homogenous, both throughout the system and over time. A mere 26 taxa comprise over 75% of the bacterial populations found in the study, as compared with the millions or billions of taxa found in more diverse environments such as soils. The dominant subway species, much like their aboveground counterparts, are a mixture of bacteria characteristic of soil, water and human skin, all relatively harmless. [A fun aside: it turns out the leading mechanism by which microbes are transferred from skin to air is through heat convection! Our body temperatures are typically greater than the surrounding air, meaning we emit a constant plume of heat carrying components of our skin microbiome]

The remarkable similarity between the microbial communities of subway air and aboveground city air is testament to a highly effective air circulation system known as “passive train pumping”. It’s the same system that causes the rush of air you feel when walking over a subway grate. According to Dr. Pace, the uniformity of microbial communities throughout the subway indicates passive train pumping is doing a good job replenishing the subway with fresh air.

PathoMap, a Weil Medical School based effort to develop a map of the New York City microbiome for pathogen monitoring and predictions

PathoMap, a Weil Medical School based effort to develop a map of the New York City microbiome for pathogen monitoring and predictions

Subway microbiome research represents one component of a larger research effort known as PathoMap. Led by  Dr. Chris Mason and his lab of microbiologists at Weil Cornell Medical School in New York, PathoMap aims to use new DNA sequencing technologies to establish “pathogen weather maps” of the city. The research group collects regular environmental samples from highly trafficked regions of NYC for microbial profiling. Microbial genomic profiles are then spatially mapped using GIS-based tools. Ultimately, Dr. Mason hopes that his maps, which track the genetic dynamics of the city’s microbiome,  will be used to detect and respond to microbial dangers, thus reducing the spread of pathogens.

The original article can be found here.

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