Scientists affiliated with MetaSUB, a global drive to chart commuter-exposed microbiomes, are currently sampling in the Stockholm subway system. The project is a unique collaboration between the Stockholm county (SLL) authority’s transit authority (SL) and Stockholm University of MetaSUB.

Researchers Klas Udekwu and Per Ljungdahl with their research teams at the Department of molecular biosciences, the Wenner-Grens institute belong to the MetaSUB consortium, sampling, identifying and visualizing microorganisms in the subway systems worldwide.

MetaSUB is an international consortium of laboratories worldwide that work on the establishment of a global DNA metagenomic map over subway systems with the ultimate goal of translating results from these studies into changes in urban design that leads to reduced spread of pathogenic microorganisms while maintaining the organismal diversity necessary for healthy living. Stockholm is one of the many cities (46 and counting) including New York, Sao Paulo, Shanghai and Moscow that will be monitored continuously over a 5 year period. Sampling will be carried out during different seasons, under varying weather conditions and volume of passenger traffic.

Where does this project lead?

Our major goal is to expand our work internationally through the MetaSUB Consortium. Our collective efforts will help future work in city planning, urban design and architecture, transit systems, public health, ecological studies, genome technologies, and improved understanding of cities.

How are we sampling?

Scientists and PhD students from Stockholm University take samples from different surfaces in subway stations and interconnecting trains. Sample collection is done with a Nylon swab that is rubbed against a surface for 3 to 5 minutes to pick up as much sample as possible and the swab is immediately packaged into a tube containing a salt solution. The sample is then documented in written and photographic form, as well as its GPS position tagged using a specific App designed for sample taking. Sampling will be done during periods of low traffic to not disturb commuters. Following this, we will extract and sequence DNA, build up a map of the microorganisms identified and further analyzed within the MetaSUB consortium, comparing this data with that from other cities.

Microorganismal diversity everywhere and everywhen.

Microorganism is the collective term for all organisms that cannot be seen with the naked eye. Bacteria and viruses are only part of this eclectic mix which also includes fungi, algae and protozoa (early animals). Most bacteria we come in contact with are from our own (and other people’s) bodies, making up our commensal flora. Their presence in our guts is known today to be required for proper development of the immune system, and even the brain. Despite this, we have only recently started to explore how increased co-habitation drives microbial community diversity and evolution and downstream effects on us.

Want to know more?

Read more on and keep track of sampling projects around the world.


Each person has their own microbial 'aura'! We each emit early 40 million bacterial cells every hour, cells that leave our skin, mouths, and other place, and find themselves in the air or landing on surfaces such as floors, walls, rails, switched, buttons, handles etc. Interestingly, even in restrooms the vast majority of these bacteria do not appear to be disease causing, and even when there are organisms that may have the potential to cause disease, no diseases are being spread. Based on this, the microbes associated with surfaces in a subway will most likely have been left their by other people, but 99.99999% of them will be like your own bacteria and won't have any effect on the individual’s health at all. Although there is no clear case of disease transmission from a subway surface, wherever people congregate, there is a chance to pick up an infection. Thanks to modern medicine, public hygiene projects, and vaccines, our subways, and other public spaces are extremely safe, but that doesn't stop viruses, especially flu or the common sold from spreading during the 'season'. To protect yourself, you really only need exercise common hygeine practices: wash your hands regularly during the season, if you have flu - stay at home. 

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