• There are countless different bacteria that live in our environment
• American researchers gathered bacteria form the shoes and cellphones of thousands of people across the USA
• A lot of the bacteria on shoes and phones of participants belong to groups called ‘microbial dark matter’ 

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Fears of the coronavirus have put germs on nearly everyone’s radar. But a new study points out just how little is known about the microbes that inhabit your environment.

You likely have thousands of different varieties of bacteria on your shoes and cellphone, including groups hardly ever studied by scientists, said researcher David Coil, of the University of California, Davis Genome Center, and colleagues.

“This [study] highlights how much we have to learn about the microbial world around us,” Coil said in a university news release.

The researchers analysed the DNA of bacteria gathered from the cellphones and shoes of nearly 3 500 people who attended sporting events across the United States.

No obvious regional trends

A consistent finding was that the shoes and phones of the same person had distinct communities of bacteria. Cellphone bacteria reflected those found on the person, while shoes had bacteria characteristic of soil. This matched previous results.

Populations of bacteria on shoes were more diverse than those on phones, according to the study.

Although samples were collected nationwide, the researchers didn’t find any obvious regional trends. In some cases, there were significant differences between samples collected at different sporting events in the same city. In other cases, samples from distant cities were quite similar.

The researchers were surprised to find that a substantial proportion of bacteria on shoes and phones came from groups called “microbial dark matter”. These bacteria are difficult to grow and study in a laboratory, so they have been compared to invisible “dark matter” believed to comprise much of the universe.

Dark matter groups of bacteria have only been discovered as scientists used genetic sequencing to search for microbes in different locations. Although many dark bacteria groups are found in remote or extreme environments – such as boiling acid springs and nutrient-poor underground aquifers – some have been discovered in more common habitats, such as soil.

“Perhaps we were naive, but we did not expect to see such a high relative abundance of bacteria from these microbial dark matter groups on these samples,” said study co-author Jonathan Eisen, of the UC Davis Genome Center.

The findings were published on 9 June in the journal PeerJ.

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