Bacterial communities on your tongue

Bacteria on your tongue aren’t just hanging around. US researchers have discovered that they actually have a complex, highly structured spatial organisation.

In fact, suggests Gary Borisy from the Harvard School of Dental Medicine: “Bacteria on the tongue are a lot more than just a random pile. They are more like an organ of our bodies.”

The image above, which was presented with a paper in the journal Cell Reports, shows bacterial biofilm scraped from the surface of a tongue and imaged using a fluorescent technique called CLASI-FISH, which Borisy and colleagues developed.

Colours indicate the human epithelial tissue that forms a central core (grey) and different bacteria: Actinomyces (red) occupy a region close to the core; Streptococcus (green) is localised in an exterior crust and in stripes in the interior. 

Other taxa (Rothia, cyan; Neisseria, yellow; Veillonella, magenta) are present in clusters and stripes that suggest growth of the community outward from the central core.

In all, the researchers analysed samples from 21 healthy participants and identified 17 bacterial genera that were abundant on the tongue and present in more than 80% of individuals. 

“Our study is novel because no one before has been able to look at the biofilm on the tongue in a way that distinguishes all the different bacteria, so that we can see how they arrange themselves,” says Borisy, the paper’s senior author.

“The tongue is particularly important because it harbours a large reservoir of microbes and is a traditional reference point in medicine: ’stick out your tongue’ is one of the first things a doctor says,” adds co-author Jessica Mark Welch.