Open Wide: Human Mouth Bacteria Reproduce through Rare Form of Cell Division

One of the most diverse ecosystems on the planet is closer than you think — right inside your mouth. Your mouth is a thriving ecosystem of more than 500 different species of bacteria living in distinct, structured communities called biofilms. Nearly all of these bacteria grow by splitting [or dividing] into two, with one mother cell giving rise to two daughter cells.

New research from the Marine Biological Laboratory (MBL) and the American Dental Association Forsyth Institute (ADA Forsyth) uncovered an extraordinary mechanism of cell division in Corynebacterium matruchotii, one of the most common bacteria living in dental plaque. The filamentous bacterium doesn’t just divide, it splits into multiple cells at once, a rare process called multiple fission. The research is published this week in Proceedings of the National Academy of Sciences.

The team observed C. matruchotii cells dividing into up to 14 different cells at once, depending on the length of the original mother cell. These cells also only grow at one pole of the mother filament—something called “tip extension.”

C. matruchotii filaments act as a scaffolding within dental plaque, which is a biofilm. Dental plaque is just one microbial community within an immense population of microorganisms that live in and coexist with a healthy human body—an environment known as the “human microbiome.” This discovery sheds light on how these bacteria proliferate, compete for resources with other bacteria, and maintain their structural integrity within the intricate environment of dental plaque.

“Reefs have coral, forests have trees, and the dental plaque in our mouths has Corynebacterium. 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,” said paper co-author Jessica Mark Welch, senior scientist at ADA Forsyth and adjunct scientist at the MBL.

“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,” said Scott Chimileski, MBL research scientist and lead author on the paper.

The Microbial Forest

This research builds off of a 2016 paper that used an imaging technique developed at the MBL called CLASI-FISH (combinatorial labeling and spectral imaging fluorescent in situ hybridization) to visualize the spatial organization of dental plaque collected from healthy donors. This earlier study imaged bacterial consortia within dental plaque, which are called “hedgehogs” due to their appearance. One of the major findings from that original paper was that filamentous C. matruchotii cells acted as the basis of the hedgehog structure.