This is where the bacteria live in the cells of the tongue!

Countless numbers of microbes inhabit the human tongue, and scientists have now taken a look at the neighborhoods bacteria build for themselves; The germs grow in thick films, with different types of microbes clustered in patches around individual cells on the surface of the tongue, the researchers report. This pattern suggests that individual bacterial cells first attach to the surface of tongue cells and then grow in layers as they form larger clumps, creating miniature environments that different species need to thrive.

Methods to identify microbial communities often look for genetic fingerprints of various types of bacteria; the techniques can reveal what lives on the tongue, but not how the bacterial community is organized in space, so the scientists had people scrape the top of their tongues with plastic scrapers, then the team labeled several types of bacteria in the dirt of the tongue with fluorescent markers of different colors to see how the microbial community was structured.

Bacterial cells largely grouped by type, in a thick, densely packed biofilm, covered every cell on the tongue surface, although the overall mosaic appearance of the microbial community was consistent between cells from different samples and people. The specific composition of the bacteria varied, according to biologists, but some bacteria were common in almost all the samples and tended to occupy roughly the same regions around the tongue cells.

The Actinomyces bacterium, for example, was typically in the center of the structure, close to the human cell; Rothia, on the other hand, tended to exist in large patches towards the outside of the biofilm, and Streptococcus formed a thin outer shell. Two of these groups, Actinomyces and Rothia, may be important in converting dietary nitrate, a compound abundant in leafy green vegetables, into nitric oxide, which dilates blood vessels and may help regulate blood pressure.

Knowing how different bacterial groups are arranged spatially on the tongue could help uncover how microbes might work together to maintain their environments and keep their host healthy.

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