Cavity-causing microbes can form crawling superorganisms

A cross-kingdom partnership between bacteria and fungi can result in the two joining to form a "superorganism" with unusual strength and resilience. Found in the saliva of toddlers with severe childhood tooth decay, these assemblages can effectively colonize teeth. They were stickier, more resistant to antimicrobials, and more difficult to remove from teeth than either the bacteria or the fungi alone, according to the research team, led by University of Pennsylvania School of Dental Medicine scientists.

What's more, the assemblages unexpectedly sprout "limbs" that propel them to "walk" and "leap" to quickly spread on the tooth surface, despite each microbe on its own being non-motile.

After seeing the bacterial-fungal clusters present in the saliva samples the researchers were curious how the groupings might behave once attached to the surface of a tooth.

They thus created a laboratory system to recreate the formation of these assemblages, using the bacteria, fungi, and a tooth-like material, all incubated in human saliva. They found a highly organized structure with bacterial clusters attached in a complex network of fungal yeast and filament-like projections called hyphae, all enmeshed in an extracellular polymer, a glue-like material.

Next the team tested the properties of these cross-kingdom assemblages once they had colonized the tooth surface and found "surprising behaviors and emergent properties," said the author, "including enhanced surface adhesion, making them very sticky, and increased mechanical and antimicrobial tolerance, making them tough to remove or kill."

When the research team allowed the assemblages to attach to and grow on real human teeth in a laboratory model, they found more extensive tooth decay as a result of a rapidly spreading biofilm.

Reference:

Hyun (Michel) Koo, Interkingdom assemblages in human saliva display group-level surface mobility and disease-promoting emergent functions,Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2209699119