Mothers around the world have got it right: every one of us is special. We all have our own unique talents, skills . . . and mouth bacteria.
More than 600 microbe species live in our saliva. Few of these are shared from person to person, and your neighbor's mouth is likely to be just as different from yours as the mouth of someone on the other side of the Earth, according to a study Thursday in the journal Genome Research
"That was surprising to us," said co-author Mark Stoneking of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "We expected, given all the variation in diet and culture around the world, that we'd see some differences."
The scientists took saliva samples from a total of 120 people in North and South America, Europe, Asia, and Africa. By sequencing and analyzing genes in the saliva, they identified 101 known bacterial genera, including 39 that had never been found in the mouth before. In addition, the researchers found at least 64 unknown genera.
"We wanted to look at global diversity in saliva, because no one's done that before," Stoneking said.
Mouth microbe makeup varied greatly from person to person, but not in any geographically structured way. Two people from Louisiana were likely to be as different as a Bolivian and a South African.
The lack of any geographic pattern suggests that scientists hoping to learn about human populations might want to stay out of the mouth. Other studies have reconstructed ancient human migrations by analyzing regional differences in certain gut bacteria. But such research requires stomach biopsies, and Stoneking and his colleagues hoped salivary bacteria could provide a less invasive alternative.
"We're still hopeful," Stoneking said. "If we were to look at variation within particular bacteria, we might find some differences. That's what we're trying to do now."
The results also help establish on a broad scale what bugs should be present in a healthy person's mouth, which could be important in future disease scans.
"Saliva is an easy thing to sample," said Ruth Ley of Cornell University, who was not involved in the study. "It's worth finding out if it can be used as a biomarker for a disease state or a predisposition to one. And for that, baseline 'normal' data are important."��
Also important is the reminder that microorganisms populate our every nook and cranny.
"This study confirms that the amount of microbial diversity on and in our bodies is really impressive," said Noah Fierer of the University of Colorado, who led research last year that found the human hand hosts on average 150 different bacteria species. "We're basically a walking microbial ecosystem."
In fact, the argument could be made that we're more microbe than human. Scientists estimate that microorganisms living on and inside us outnumber human cells more than 10 to one.
"A lot of people get freaked out when they hear that," Fierer said. "But a lot of microbes are either completely innocuous or beneficial."
Some gut bacteria, for example, stimulate immune-system development, help us digest carbohydrates and fats, and synthesize vitamins for us. These creatures have co-evolved with us for eons, and their biology is inextricably tied to ours. And in many cases, we don't even know their names.
But that's changing. In 2007, the National Institutes of Health pledged $115 million to catalogue the myriad microbes that make us their homes. The resulting Human Microbiome Project started last year. Similar efforts are underway in Europe and Asia as well. A better understanding of our rich microbiota, the reasoning goes, can only improve human health in the future.
A recent study, for example, found that obese and lean people have different bacterial communities living in their guts. When obese people lost weight, their microbe profiles shifted to look more like those of the lean. Knocking out the weight-gainer species could help curb the world's obesity epidemic.
Other gut-bacteria imbalances are tied to cancer, asthma, and autoimmune diseases.
See Also:
- Gut Bacteria Affect Almost Everything You Do
- Gut Bacteria, Language Analysis Solve Pacific Migration Mystery ...
- A Rule of Thumb for Gut Bacteria
- Low-Calorie Longevity May Be Linked to Gut Bacteria
- Internal Bacterial Imbalance Leads to Asthma
Citation: "Global Diversity in the Human Salivary Microbiome." By Ivan Nasidze, Jing Li, Dominique Quinque, Kun Tang, Mark Stoneking. Genome Research Vol. 19, March 2009.
Image: Flickr/foxtongue
