Bacteria and fungus can join forces to wreak havoc on your teeth, according to a somewhat serendipitous discovery.
When examining the microbes that cause aggressive tooth decay in young children, Zhi Ren, a dental researcher from the University of Pennsylvania, noticed two distinct organisms that present a single front under the microscope.
Further research in the laboratory investigated how these bacterial-fungal swarms in human saliva could work together in the mouth to cause tooth decay disease.
The findings reveal several “emerging functions” of the clusters, which make the species function almost like an entirely new superorganism – including new abilities to move and spread in our teeth.
Conjugated pathogens were caught doing things they could not otherwise accomplish on their own.
The normally sedentary bacteria, Streptococcus mutans, they were no longer bound to the vagaries of saliva. Hitchhiking on the outstretched arms of yeast, Candida albicansthe bacteria could now move by “jumping”, constantly increasing as they spread.
“This discovery of a ‘bad’ superorganism is truly groundbreaking and unexpected,” says microbiologist Knut Drescher from the University of Basel in Switzerland.
“No one would have predicted this.”
It’s not like bacteria and fungi haven’t been found working together before. Multicellular biofilms cause many human infections. It is more that our knowledge of how these communities develop and function remains limited.
In the laboratory, the authors of the current study discovered that clusters of bacteria can attach to the body, branches, and external sugars of fungal yeasts.
As a group, this cellular network can more easily attach to teeth than the cells themselves. The “superorganism” also shows stronger tolerance to antimicrobials and brushing.
But the craziest thing is how the superorganism moves.
While some bacteria have small arms that they use to swim, S. mutans is usually stationary. Actually, neither C. albicans neither S. mutans can move as such, but because C. albicans can stretch his arms out, provides the perfect vehicle for a hitchhiker.
When bacteria attach to these probing fungal filaments, they can effectively “jump” forward to merge with other biofilms.
When they tested the superorganisms on tooth-like surfaces, the researchers found that the bacteria moved at a speed of more than 40 microns per hour, similar to the speed of movement of molecules that heal wounds in the human body.
Within hours of connecting the two pathogens, the authors caught bacteria jumping on substrates 100 microns away, a distance more than 200 times their usual body length.
As far as the team knows, no one else has reported this kind of team-wide mobility.
“Dynamic fungal-bacterial interactions lead to biofilm superstructures that cause extensive and more severe damage to the tooth enamel surface,” the authors write.
If bacteria and fungi can somehow stop attaching to each other, researchers believe it could help prevent tooth decay.
But the discovery also has significance for reasons outside of dental work.
The new findings could explain how similar superorganisms transmit infectious diseases or cause environmental contamination with such speed.
“This collective multicellular migratory mode opens up interesting possibilities,” the authors write.
“This could be a stochastic mobility mechanism used by Middle Kingdom colonists to enhance nearby range expansion or possibly a navigation strategy to a desired direction or location.”
The study was published in PNAS.