A colony of Corynebacterium matruchotii. Credit: Scott Chimileski, MBL
WOODS HOLE, Mass. — 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.
Paper Summary
Methodology
The researchers used a combination of live-cell time-lapse microscopy and fluorescent D-amino acids to visualize the growth and division of Corynebacterium matruchotii, a bacterium found in dental plaque. The bacteria were grown on agarose pads in controlled conditions that simulated the oral environment. Fluorescent markers allowed the scientists to track the incorporation of new cell wall material during cell growth and division, highlighting areas of active peptidoglycan biosynthesis. This innovative approach provided insights into how the bacteria elongate through tip extension and undergo simultaneous multiple fission to divide into several daughter cells at once. The study also involved multispecies biofilms to understand the interactions between different oral bacteria.
Key Results
The key finding of the study was that Corynebacterium matruchotii grows by elongating at one pole of the cell and then divides simultaneously into multiple daughter cells, a process known as multiple fission. The study observed that this bacterium could produce between 3 and 14 daughter cells at once, depending on the length of the original cell. This rapid division allows the bacterium to form long filamentous structures within dental plaque, which helps it compete for space and resources.
The researchers also found that the new daughter cells quickly begin to grow into thinner filaments, continuing the process of colony expansion. These unique growth and division strategies give C. matruchotii a competitive advantage in the densely populated oral microbiome.
Study Limitations
While this study sheds light on the unique cell division of C. matruchotii, it is limited by the artificial environment in which the bacteria were observed. The controlled laboratory conditions, such as agarose pads and nutrient media, may not fully replicate the complex conditions of the human mouth, where the bacteria interact with a wide range of other microbial species and environmental factors. Additionally, while the fluorescent markers provided valuable insights into cell wall biosynthesis, they may not capture every aspect of bacterial growth and division in real-time.
Discussion & Takeaways
This research contributes significantly to our understanding of bacterial growth and morphology, particularly in the context of dental plaque biofilms. The discovery that Corynebacterium matruchotii divides through multiple fission rather than the more common binary fission expands our knowledge of bacterial reproductive strategies.
These findings may have broader implications for microbial ecology, as the ability to rapidly produce multiple daughter cells could be a critical factor in how bacteria colonize and dominate certain niches. In the oral microbiome, where space and nutrients are limited, this rapid division could help C. matruchotii maintain its structural role in biofilms. The study also opens the door for further research into how bacterial morphology influences the spatial organization of microbial communities.
Funding & Disclosures
This study was supported by the NIH (National Institutes of Health) under award R01 DE022586 and the NSF (National Science Foundation) under award 2245229. The authors have declared no competing interests.
