The human mouth is more for just chewing and talking. It’s also home to over 500 different bacterial species. Like a scene out of “Osmosis Jones,” these microorganisms live in structured communities called biofilms. This complex ecosystem relies on bacteria to keep the population intact by cell division, with one mother cell splitting into two daughter cells.
However, not all bacteria follow the rules of cell division. Scientists have recently observed a unique type of cell division in Corynebacterium matruchotii (C. matruchotii), one of the main bacteria in dental plaque. Instead of dividing in two, the bacterium breaks into multiple cells, a rare process of multiple fission. The discovery was published in the journal Proceedings of the National Academy of Sciences.
Instead of dividing into two cells, the team found C. matruchotii divided into 14 at once! The cells only grow at one end of the mother filament, also known as “tip extension.” The filaments in C. matruchotii congregate together and the collection of bacteria sticking together on the surface makes up biofilm. In this case, C. matruchotii clump together within dental plaque making it one of many microbial communities in the human body.
“The Corynebacterium cells in dental plaque are like a big, bushy tree in the forest; they create a spatial structure that provides the habitat for many other species of bacteria around them,” says Jessica Mark Welch, a senior scientist at ADA Forsyth and adjunct scientist at The University of Chicago’s Marine Biological Laboratory, in a media release.
“These biofilms are like microscopic rainforests. The bacteria in these biofilms interact as they grow and divide. We think that the unusual C. matruchotii cell cycle enables this species to form these very dense networks at the core of the biofilm,” adds Scott Chimileski, a research scientist at MBL and lead author of the new study.
C. matruchotii is different from other bacterial species because it does not have flagella. These are thin, hair-like appendages that help bacteria move around. Without this, bacteria cannot freely move around. To compensate, the researchers believe C. matruchotii’s evolved multi-cell division and an elongated body to explore their surroundings. This is similar to actions taken from mycelial networks in fungi and Streptomyces bacteria in soil.
“If these cells have the ability to move preferentially towards nutrients or towards other species to form beneficial interactions — this could help us understand how the spatial organization of plaque biofilms comes about,” says Dr. Chimileski.
The new findings expand on previous research studying how C. matruchotii cells survive, compete for resources with other resources, and help build the complex microbial community found in dental plaque. In a 2016 paper, the researchers used an imaging technique called CLASI-FISH (combinatorial labeling and spectral imaging fluorescent in situ hybridization) to map out how the organized layers in dental plaque from healthy donors. The plaque had a unique “hedgehog” appearance because of the bacteria clumped together. One main finding was C. matruchotii cells acting as the foundation for the hedgehog structure.
Dentists recommend brushing your teeth twice a day, which helps remove dental plaque. However, the biofilm always comes back, no matter how often you brush. Scientists now understand it’s because of C. matruchotii’s unusual cell division strategy. When scientists measured cells, they found C. matruchotii colonies could grow up to half a millimeter per day.
There are other Corynebacterium species living in the human body, such as on the skin and inside the nasal cavity. However, they do not have the same appearance and ability to divide via multiple fission.
“Something about this very dense, competitive habitat of the dental plaque may have driven the evolution of this way of growing,” Chimileski concludes.
The next challenge is figuring out how the evolution of this bacterial reproductive strategy affects our mouths and the rest of the body.
Source: https://studyfinds.org/dental-plaque-bacteria-rainforest/?nab=0
