Lately, we've been learning more and more about the teeming masses of bacteria inside our bodies - essentially trillions of tiny organisms that make us sick and keep us healthy.
Now two scientists at the University of Colorado have dared to ask what kinds of bacteria lives inside our mouths. And they're finding some pretty surprising things in there.
Ken Krauter, a professor of microbiology, and Simone Stahringer, a graduate student, took oral bacteria samples from 45 sets of twins and sequenced the bacteria's DNA. They thought that identical twins would have similar types of bacteria living in their mouths, because identical twins share the same genetic make-up.
They were wrong.
The identical twins' bacteria was not any more similar than the bacteria living in the mouths of fraternal twins, who only share half of their genes. Furthermore, Krauter and Stahringer, whose findings were published this week in the journal Genome Research, found that when identical twins stop living together in the same house, their oral bacteria became a bit more distinct.
What this tells us, Krauter said, is that, unlike in other parts of the body, oral bacteria is determined by environment, not genes.
"[We thought] that the human genome or your immune system or the surfaces of your mouth would have a profound affect on which microbes would choose to live in your mouth," Krauter said. "But that wasn't really the case. The most abundant bugs that are living in your mouth are dependent on what you eat, who you kiss, how often you brush your teeth."
At the same time, bacteria in the mouth is generally more homogenous than the bacteria in the gut, where there are communities of bacteria unique to individuals. Most of the bacteria in the human mouth can be grouped into eight basic types, Krauter says.
Those oral bacteria that fall outside of these eight types - the outliers, as he called them - may cause disease. But Krauter says if we can find a way to identify them, scientists could figure out ways to fight them.
But Krauter and Stahringer have a long way to go before they can take their work out of the lab and into the doctor's office. Right now, they're just trying to figure out exactly what is living in our mouths.
Figuring out how those they work for or against us will have to come later.