Every city in the world has its own microbiome!

Public transport is home to tens of thousands of viruses and bacteria, 97% of which are specific to each city. An invisible microbiome of incredible biodiversity.

« Give me your shoes and I’ll tell you 90% of the town you come from Christopher Mason smiles. This ETH Zurich researcher and his colleagues created the largest database viruses and bacteria present In public transports from 60 cities around the world, including Marseille, London, New York, Sydney and Hong Kong. They took 4,728 samples over three years and identified nearly 14,000 cash from microbes. « Most people think of the rainforest as the best place for biodiversity. But our study shows that a subway bench can be just as rich in microbes! », Confirms Christopher Mason.

80% unknown viruses

Even more amazing: each city has its own microbiome, which in a way represents its “molecular signature”, explains Christopher Mason. If there is a “heart” of 31 microbes common to 97% of cities, most species are specific to a single location. So specific that of these 14,000 species, only 4,246 had already been identified. No less than 10,928 viruses and 748 species of bacteria, on the other hand, were completely unknown, and did not appear in any database!

However, do not think that you are in great danger walking the corridors of the metro: most of these microbes are harmless to humans. ” Almost all viruses are bacteriophages, that is, they attack bacteria », Testifies in the New York Times David Danko, one of the co-authors of the article published in the journal Cell. « We are in constant contact with all these microbes and they are part of the ecosystem in which we live », Assures the researcher. The human body would also shelter itself nearly 38,000 billion bacteria in his gut, hair or skin, more than the number of human cells!

Mostly human bacteria

It is therefore quite logical that among the microbes present in theair and on the surfaces of the cities, one finds in majority bacteria living in the human being, and especially those of the skin. This includes for example Cutibacterium acnes, which feeds on sebum, or Micrococcus luteus, responsible for body odor. The researchers also found bacteria living in the soil, and more surprisingly, bacteria usually found in the ocean. Most of these city microbes actually share a high level of resistance. « A metro rail in steel is probably not a pleasant place to live, but these species have adapted to live in these inhospitable environments », Explains Christopher Mason.

A “microbial signature” unique to each city

Researchers, on the other hand, have a harder time explaining the huge differences between cities. The weather and geography certainly play an important role, but it mostly depends on the people who live there. Previous studies have shown that each individual has a unique microbiome, depending on age or diet. The “microbial signature” of a city would thus be a mixture depending on multiple factors, such as the food found there, the factories present, the nature of the surrounding soil, or even practices. matter hygiene.

These 14,000 microbes are only the beginning, however. After the subways, researchers set out to take samples from hospitals, waste and public spaces. ” This work will not only help detect future agents pathogens, but could also help to develop future molecules therapeutic », Confirms Christopher Mason.

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