A cross-kingdom partnership between bacteria and fungi can result in the two joining to form a "superorganism" with unusual strength and resilience. It may sound like science fiction, but these microbial groupings are very much part of the here and now.
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 a 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, the team reported in the Proceedings of the National Academy of Sciences.
"This started with a very simple, almost accidental discovery, while looking at saliva samples from toddlers who develop aggressive tooth decay," says Hyun (Michel) Koo, a professor at Penn Dental Medicine and a co-corresponding author on the paper. "Looking under the microscope, we noticed the bacteria and fungi forming these assemblages and developing motions we never thought they would possess: a 'walking-like' and 'leaping-like' mobility. They have a lot of what we call 'emergent functions' that bring new benefits to this assemblage that they could not achieve on their own. It's almost like a new organism—a superorganism—with new functions."
In the past, Koo's lab has focused on the dental biofilm, or plaque, present in children with severe tooth decay, discovering that both bacteria—Streptococcus mutans—and fungi—Candida albicans—contribute to the disease.
The new set of discoveries came about when Zhi Ren, a postdoctoral fellow in Koo's group, was using microscopy that allows scientists to visualize the behavior of living microbes in real time. The technique "opens new possibilities to investigate the dynamics of complex biological processes," says Ren, a first author on the paper and part of the first cohort of the NIDCR T90R90 postdoctoral training program within Penn's Center for Innovation & Precision Dentistry.
Because these assemblages are found in saliva, targeting them early on could be a therapeutic strategy to prevent childhood tooth decay, says Koo. "If you block this binding or disrupt the assemblage before it arrives on the tooth and causes damage, that could be a preventive strategy."
