Microbes are everywhere in our guts—and in our mouths. Now, a new study reveals our tongue-dwelling companions aren’t all mixed together randomly; instead, they seem to prefer living close to their own kind, separating out into distinct groups based on their species.
Researchers started by scraping the tongues of 21 healthy human volunteers. Then, they used fluorescent tags to identify specific groups of bacteria, some of which produce nutrients for us, so they could see exactly where each one lived on the tongue’s surface. Without exception, the bacteria formed tight-knit, well-defined clusters of the same species, the researchers report today in Cell Reports.
The clusters (above) resemble a microbial rainbow under the microscope. For instance, Actinomyces bacteria, in red, grow close to the epithelial tissue of the tongue, shown in gray, while Rothia bacteria, in cyan, form long patches between other communities. Streptococcus, in green, form a thin crust on the edge of the tongue and slender veins in the interior. By looking at the images, the researchers could guess at how these colonies establish themselves and grow over time.
Although scientists already know much from DNA sequencing about which microbes live in the human body, this is the first time they have been able to observe the microbial communities of the tongue in such detail. Seeing where the different species congregate and how they organize themselves can reveal much more about how the bacteria function, the researchers say, and how they interact with one another.