New research out this week confirms that our subways aren’t just jam-packed with people—they’re also filled to the brim with viruses, bacteria, and other microbes. Using samples from transit stations in 60 countries, scientists have created a microbial atlas of sorts. But though the scientists have discovered lots of previously unknown species living in these subways, people shouldn’t be too worried about the tiny commuters that they’re spending time around.
The new study is the culmination of a years-long effort by a large team of researchers from all over the globe as part of a project called MetaSUB. Their goal: To map the metagenomics of the world’s major subways and other city environments. Metagenomics is a way for scientists to get a bird’s eye view on the microorganisms that live in a particular environment. To do this, they analyze all of the DNA found in a sample (for example, a cotton swab of a pole from a New York subway), then try their best to figure out where it likely came from. Some bits will clearly belong to bacteria, some will come from viruses, and others may be from the cells of larger animals, including people.
There have been other attempts to study the microorganisms that take the train, but none quite as large as this. To create their map, the researchers collected more than 4,000 samples from 60 cities over the course of three years. In these samples, they came across 4,246 species of microbes known to exist already. In addition, they identified a core of 31 species universal to subways, with lots of variation elsewhere between cities. But they also estimated finding 10,928 viruses and 748 bacteria never before documented.
The findings, published in Cell on Wednesday, are the latest to show that cities really do contain their own unique microbial communities, or microbiomes, which are separate from the microbiomes found in soil or inside our bodies. And they reveal just how much we still don’t know about these hidden neighbors of ours and the world they live in.
“Much of the urban microbiome likely represents previously unobserved diversity, as our samples contain a significant proportion of unclassified DNA,” the authors wrote.
The team identified plenty of genes that help bacteria resist antibiotics. Some resistance genes can be passed directly between bacteria, further raising the risk that disease-causing germs will become better at adapting to our weapons. But the researchers are quick to point out that nearly all the microbes they found are certain to be harmless to people.
“We don’t see anything that we are worried about,” study author David Danko, a microbiologist at Cornell University and director of bioinformatics at MetaSUB, told the New York Times. “We don’t want people to be scared of these microbes, because these are just part of the ecosystem that we as humans live in.”
It’s possible that the viruses and bacteria found in the world’s various subway systems could actually help us down the line since there may be clues in their biology that could advance the development of new drugs or other technologies. And the researchers hope MetaSUB can be the first critical step toward creating a broad surveillance network of the world’s microbes, one that could allow us to stay ahead of current crises like antibiotic resistance as well as potential threats like the next pandemic.
“Indeed, a continually updated, global microbial genetic atlas has the potential to aid physicians, public health departments, government officials, and scientists in tracing, diagnosing, and predicting epidemiological risks and trends,” they wrote.