In the field of medical research the human mouth is often referred to as “biological dark matter,” due to the stubbornness of the bacterium found in this part of the body. The majority of bacteria in the mouth are extremely difficult to grow in a laboratory dish, and as a result most of them have never been named, classified, or studied extensively.
Fortunately a group of scientists at Ohio State University has managed to sequence the genome of one of these bacterium; Tannerella BU063. The bacterium is listed as “most wanted” by the Human Microbiome Project, which continually works towards developing our understanding of the microbial organisms that affect human health and disease.
This breakthrough is beneficial due to BU063’s close relation to the pathogen Tannerella Forsythia, a bacterium that is directly related to the gum disease periodontitis. Researchers have selected the genes that are present in Forsythia but not BU063 as strong candidates for continued study.
“One of the tantalizing things about this study was the ability to do random searches of other bacteria whose levels are higher in periodontitis,” said Clifford Beall, lead author of the study. “We looked for genes that were present in these bacteria and forsythia and not in BU063. There is one particular gene complex in a whole list of these periodontitis-related bacteria that could be involved with virulence.”
Periodontitis is a serious gum disease that results from extensive inflammation and infection of the gums. Pockets filled with a multitude of bacteria from between the teeth and gums and cause damage to the bone that acts as a support structure. Due to the excessive varieties of bacteria related to the disease, antibiotics are considered ineffective, meaning treatment usually takes the form of deep cleaning and surgery.
The lack of knowledge surrounding these bacteria leaves their characteristics a mystery.
“Basically the circumstances surrounding periodontitis aren’t very well understood,” said Beall.
“There are a lot of different bacteria that are higher in periodontitis lesions, but we don’t see every one of those bacteria in every case of periodontitis. So it’s hard to see a drug affecting one bacteria being very successful.”
Researchers from the Oak Ridge National Laboratory collected an oral material sample from the mouth of one healthy person for the study. They sorted twelve individual BU063 bacterial cells and made copies before delivering them to their colleague at Ohio State. Beall then sequenced the genomes of the dozen cells and used both individual cells as well as groups to construct a complete genome for BU063.
The research showed that, despite BU063’s incredible similarity to Forsythia, they still share a 44 percent difference in their gene makeup. The absence of particular genes in BU063 that are present in Forsythia supports an existing theory that three genes may be responsible for forsythia’s disease-causing ability.
Through comparisons to other organisms that are directly related to chronic periodontitis, Beall managed to identify a gene cluster that is present in all of these pathogens except for the BU063 genome. The findings of this study will contribute to the Human Microbiome Project’s mission of characterizing the microbial communities in the mouth and other parts of the body.
Visit Dr Andrew Hall at his Colorado Springs dental clinic to more about Periodontitis.