Our body is not only ours: it is the habitat in which thousands of microorganisms live, feed and reproduce. Some are beneficial to us and help us perform our basic functions, others do not affect us, and a few cause us problems when there is some kind of imbalance.
One of these communities, that of our language, forms a very complex ecosystem, a whole microbial universe with a very precise structure. Although the components of this particular world are more or less well known, until now less attention has been paid to its spatial organization. Are microorganisms distributed randomly or rather can we assign areas in which each specific group ‘resides’, so to speak?
The spatial organization of these miniature cities is affected by variables such as temperature, humidity, saliva flow, pH, oxygen and the frequency of disturbances such as the arrival of toothpaste and other oral hygiene products. . Additionally, microbes influence their neighbors by acting as sources and sinks for metabolites, nutrients, and molecules. By taking up space, microorganisms can physically exclude each other from desirable habitats, but their surfaces also have binding sites to which other microbes can adhere.
Now, a team of researchers has just published in the journal Cell Reports a series of images, obtained with a new fluorescence imaging technique, that show the spatial organization of the tongue microbiome with very good resolution. To make these unique maps, the scientists used samples from the tongue scraping of 21 people, and were able to identify the 17 most abundant genera of microorganisms, all present in at least 80% of the study participants.
A very well defined organization
The team was able to identify three types of samples: bacteria that live freely, bacteria attached to the epithelial cells of the tongue, and bacteria organized in consortia, which would be a kind of structurally very complex biofilms made up of multiple layers. The study of these consortia is very interesting: they were generally dominated by a specific type of microorganism, organized around a nucleus of epithelial cells and with a very well defined perimeter.
The results further revealed that the languages of all participants showed consortia of three main bacterial genera: Actinomyces, Rothia, and Streptococcus . Actinomyces frequently appeared near the nucleus, while Rothia was often seen in large patches towards the outside of the consortium. In turn, the streptococci formed thin crusts on the outside of the pools and veins or patches on the inside.
For the authors, these results give us an idea of how these well-structured bacterial communities are formed. First, the bacteria attach to the surface cells of the tongue (this layer is called the epithelium), and they do so individually or in groups. As the community grows, the different types of bacteria compete with each other, so that each group ends up proliferating more in the microenvironments that best meet their physiological needs. This differential growth results in this patchwork mosaic organization seen in mature consortia.
Bacteria, our allies
Other information that can be inferred from the spatial organization of the bacterial communities of the tongue has to do with the reduction of nitrates, a function that is not encoded in the human genome and that, therefore, we are not able to perform for ourselves. themselves. The images revealed that some genera that do have this ability, such as Actinomyces, Neisseria, Rothia, and Veillonella , are prominent in language consortia. This raises the possibility that some of the small bumps on the surface of the tongue are structured in a way that encourages the growth of bacteria that convert nitrate in saliva to nitrite.
“Understanding who lives next to whom in these communities will help us understand how they work,” explained Jessica Mark Welc, one of the authors. “The tongue is particularly important because it houses a large reservoir of microbes and is a traditional reference point in medicine. One of the first things a doctor tells you in the office is precisely: ‘Stick your tongue out'”, he concludes.
Explanation of the upper image: human epithelial tissue forms a central nucleus (gray). The colors indicate different bacteria: Actinomyces (red) occupies a region close to the nucleus; Streptococcus (green) is located in the outer cortex and forming stripes on the inside. Other taxa (Rothia, cyan; Neisseria, yellow; Veillonella, magenta) are present in groups and bands that suggest that the community grows outward from the central nucleus.
Referencia: Wilbert et al. 2020 “Spatial Ecology of the Human Tongue Dorsum Microbiome” Cell Reports.
