In one of the largest studies of this kind, researchers in the US analyzed the microbial communities that live on our phones and in our shoes.

“This highlights how much we have to learn about the microbial world around us,” said David Coil, a researcher at the University of California, Davis Genome Center and first author on the paper published in the journal PeerJ.

Microbes have a bad reputation, but that’s not entirely deserved. Every single day, you carry around a large community of microbes, most of which are completely harmless — or even beneficial. We all have our own personal microbiome, but we’re only just starting to learn about this.

In 2013, a group of researchers wanted to find out more about this community of microbes, especially two groups of microbes: those on our shoes and those on our phones. Russell Neches and Professor Jonathan Eisen of the UC Davis Genome Center, UC Davis graduate student and professional cheerleader Wendy Brown, Darlene Cavalier of Science Cheerleaders, Inc. and colleagues swabbed samples from the shoes and phones of over 3,000 people, characterizing the microbes they found.

Although samples were collected all across the US, the researchers did not find any clear regional trends. In some cases, there were big differences between samples taken in the same city, while some samples from distant cities looked very similar.

But researchers still report some trends.

For instance, shoe microbes were more diverse than those found on a person’s phone. Also, as expected, phone microbes tended to resemble people’s microbiome, while shoe microbes resembled the microbiome found in soil.

Surprisingly, a substantial proportion of the observed bacteria came from so-called “microbial dark matter.” These microbes are difficult to find and study, which led biologists to compare them to the invisible “dark matter” that astronomers think makes up much of the universe, but can’t really study. Often, these dark matter microbes are found in extreme environments such as near volcanoes or in acid springs, but they are sometimes found in more mundane environments, like urban soil.

Nevertheless, researchers were surprised to find so many bizarre microbes — up to 10% of samples contained dark microbe groups.

“Perhaps we were naïve, but we did not expect to see such a high relative abundance of bacteria from these microbial dark matter groups on these samples,” Eisen said.

“A remarkable fraction of people are traveling around with representatives from these uncultured groups on commonplace objects,” Coil added said.

The microbial survey could be interesting both from an epidemiological perspective and in the emerging field of microbial forensics — our individual microbial community could be an identifiable fingerprint.

The study has been published in PeerJ.