Myriad microbes dwell on
human tongues — and scientists have now
gotten a glimpse at the neighborhoods that bacteria build for themselves.
Bacteria grow in thick films,
with different types of microbes clustered in patches around individual cells
on the tongue’s surface, researchers report online March 24 in Cell Reports. This pattern suggests
individual bacterial cells first attach to the tongue cell’s surface and then grow
in layers as they form larger clusters — creating miniature environments the different
species need to thrive.
“It’s amazing, the complexity of
the community that they build right there on your tongue,” says Jessica Mark Welch, a microbiologist at the
Marine Biological Laboratory in Woods Hole, Mass.
Methods to identify microbial
communities typically hunt for genetic fingerprints from various types of bacteria (SN: 11/05/09). The techniques can reveal
what lives on the tongue, but not how the bacterial community is organized in
space, Mark Welch says.
So she and her
colleagues had people scrape the top of their tongues with plastic scrapers.
Then the team tagged various types of bacteria in the tongue gunk with differently
colored fluorescent markers to see how the microbial community was
Bacterial cells, largely
grouped by type in a thick, densely packed biofilm, covered each tongue
surface cell. While the overall patchwork
appearance of the microbial community was consistent among cells from different
samples and people, the specific composition of bacteria varied, Mark Welch
But some bacteria were
common across nearly all samples and tended to occupy roughly the same regions
around tongue cells. Actinomyces bacteria,
for example, were typically at the core of the structure, close to the human
cell. Rothia, on the other hand,tended to exist in large patches toward
the outside of the biofilm and Streptococcus
formed a thin outer layer. Two of these groups —
Actinomyces and Rothia — may be
important for converting dietary nitrate, a compound abundant in leafy green
vegetables, to nitric oxide, which dilates blood vessels and can help regulate
Knowing how different bacterial groups are spatially arranged on the tongue could help uncover how the microbes might work together to maintain their environments and keep their host healthy (SN: 2/18/16).