American researchers Tuesday published the first major results from a crowdsourced, global citizen science project on the human microbiome for which over 10,000 participants had mailed in their poop and spit.
The American Gut Project, as described in the journal mSystems, an open access journal from the American Society for Microbiology, is the largest published study to date of the unique microbial communities that inhabit human bodies.
"We observed a much greater microbial diversity than previous smaller studies found, and that suggests that if we look at more populations, we'll see more diversity, which is important for defining the boundaries of the human microbiome," said Daniel McDonald, scientific director of the American Gut Project at University of California (UC), San Diego School of Medicine.
The project, founded in November 2012, is designed to better understand human microbiomes: which types of bacteria live where, how many of each, and how they are influenced by diet, lifestyle and disease.
To do this, citizen scientists contribute 99 U.S. dollars and receive a kit to collect a fecal, oral or skin swab and instructions to mail it back. Once the sample is processed, participants receive a report that details what's living in their guts or other body site.
Also, each participant would answer a voluntary survey that includes questions about general health status, disease history, lifestyle and diet.
As of mid-2017, the project included microbial sequence data from 15,096 samples provided by 11,336 people, representing primarily the United States, Britain and Australia, along with 42 other countries or territories.
"It's really amazing that more than 10,000 people ... have mailed their poop to our lab so that we can find out what makes a difference in somebody's microbiome," said Rob Knight, the project's founder who is also a professor at the UC San Diego School of Medicine.
To tease out the identities of the bacteria living in a participant's mixed sample, the American Gut Project team sequences a genetic marker unique to bacteria and archaea.
Called 16S rRNA, this molecule acts as a sort of barcode for these microbes. For the thousands of samples, they also used metabolomics to identify the non-living molecules and chemicals.
The study found that various factors play a role in the diversity of the human gut microbiome, such as diet, the use of antibiotics or mental health.
However, the researchers said most of the findings so far were simply observations or associations, and in many cases researchers could not extrapolate the ultimate effect on human health.
"The human microbiome is complex, but the more samples we get, the sooner we will be able to unravel the many ways the microbiome is associated with various health and disease states," Knight said.
McDonald said living datasets like this will allow researchers to document the slow but steady global homogenization driven by increased travel, lifespans and access to similar diets and therapies, including antibiotics.