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July 11, 2016

Could microbes evolving on subway systems one day kill us all?

By Emily Reynolds

The tube has many qualities. It’s hot. It’s often intolerable. It increases your likelihood of having face-armpit contact with a sweaty businessman before 9am by around 450 per cent. It has a dubious range of retro seat patterns.

What it is definitively not, however, is “sterile”.

As with almost everything that exists in the known universe – including, I’m sorry to inform the more squeamish among you, the human body – subway systems are absolutely teeming with various types of bacteria. And the way our bodies, with their mildly terrifying bacterial/human cell ratio of 10:1, interact with and acquire those bacteria all depends on the environments we live in. With so many people commuting every day, and around 54 percent of the world’s population living in a major city, there’s one very obvious source of these environmental microbes: subway systems.

So to understand this vibrant but invisible ecosystem of microorganisms (otherwise known as the microbiome), a multidisciplinary team from across the world has decided to map it in a project they’ve called MetaSub. MetaSub takes all of this microbial information, analyses it and creates a unique map of individual subway systems.

Christopher Mason, an associate professor at Cornell Medicine, told me that the inspiration for MetaSub came from watching his daughter, as toddlers tend to do, “put everything in her mouth”. As a father, and also, probably, as a leading expert on genomics, he wondered what, exactly, she was putting in her mouth. Spoiler alert: it was a not insignificant amount of environmental bacteria.

After the first attempt at mapping the microbiome of the New York subway, his team realised “how useful the data could be for discovering the shorelines of unknown continents of DNA, as if explorers in 1491”. They’ve now established unique microbial profiles of 15 global subway systems including New York, Paris, Beijing, Mexico City and, most recently, Barcelona; there’s an interactive map showing where researchers have taken samples.


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Sample collection is pretty simple. Researchers make extensive swabs on different areas of the subway, including seats, handrails, escalators and carriage floors. The samples are then subject to DNA sequencing and “metagenomic analysis”, meaning that genomes are sequenced both in their entirety and individually. These can then be analysed and compared to known bacteria.

In one of the first trials of the project, the team found that 48 percent of the bacteria measured on the New York subway “did not match any known organism”. This, the team say, underscores the “vast wealth of likely unknown organisms that surround passengers every day”, and is either incredibly cool or incredibly terrifying depending on how you look at it.

The data currently being gathered by the project could potentially help create a “smart city” – one that that uses multi-level data to improve city planning, management and human health.  Long term, MetaSub also hopes to discover new genes and organisms, create forensics maps, understand detailed densities of global anti-microbial resistance markers, and maybe even create new drugs to combat some of the nastier strains of bugs.  More seriously, the maps could also be used for what Mason calls “the biosurveillance of antibiotic resistant genes or pathogens” – essentially meaning they could help prevent the outbreak of some horrible, as-yet unknown infectious disease.

What this doesn’t mean, however, is that you should be wearing a Hazmat suit every time you get on the Central Line. Reassuringly, Mason notes that despite the high level of bacteria on every mass transit system they’ve mapped so far, there are relatively few diagnosed cases of infectious diseases, dispelling the belief that stations need to be hyper-clean to be safe. So put down the wet wipes – the biggest threat to your journey is probably still that dick who won’t move down the carriage.

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