Microorganisms seem to have found a home nearly everywhere on the planet, including the insides of animals. The skin, gastrointestinal tracts, lungs, and mouths of humans have been colonized by bacteria, which form microbial communities known as microbiomes in those, and other places. The microbiomes of the human body can have a powerful influence on human health. Many of those microbes have evolved to suit their environments, and have a symbiotic relationship with their hosts. There are lots of specialized molecules and processes that have been discovered among human microbiota.
Now researchers have analyzed the human mouth microbiome, and found a rare type of cell division process happening there. Usually, cells proliferate by dividing from a mother cell into two daughter cells, and that process repeats an untold number of times over generations.
But Corynebacterium matruchotii ia a common bacterium that lives in human dental plaque, and it is a filament-shaped cell in which a mother cell can split into multiple cells at once, instead of only two daughter cells. This unusual process is known as multiple fission, and depending on the length of the mother C. matruchotii cell, the researchers observed them dividing into as many as fourteen different daughter cells at once. The findings have been reported in the Proceedings of the National Academy of Sciences (PNAS).
In this study, the investigators used specialized microscopy techniques to watch the C. matruchotii filaments grow. These cells grow at only one end of the mother filament in a process called tip extension, and the researchers could watch the growth dynamics; they were found to grow as much as half a millimeter every day. The scientists were able to see how the bacterial cells in the dental microbiome interacted as well.
These hardy cells grow in the mouth regardless of how well or how much people brush. While there are other types of Corynebacterium on the skin and in the nasal cavity, they don't grow quite like those in the mouth. Skin and nasal species of Corynebacterium are shorter and don't use tip extension or multiple fission.
C. matruchotii also don't move around because they lack flagella. Its unusual modes of elongation and cell division might help the bacterium explore its environment, the study authors suggested
"Something about this very dense, competitive habitat of the dental plaque may have driven the evolution of this way of growing," noted co-corresponding study author Scott Chimileski, a research scientist at the Marine Biological Laboratory (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."
"Who would have thought that our familiar mouths would harbor a microbe whose reproductive strategy is virtually unique in the bacterial world," added co-corresponding study author Gary Borisy, a principal investigator at ADA Forsyth and former MBL director. "The next challenge is to understand the meaning of this strategy for the health of our mouths and our bodies."
Sources: Marine Biological Laboratory (MBL), Proceedings of the National Academy of Sciences (PNAS)