Study Adds To Human Microbiome Project

Scientists have pieced together sections of DNA from 12 individual cells to sequence the genome of a bacterium known to live in healthy human mouths. The researchers were able to reinforce a theory that genes in a closely related bacterium could be culprits in their ability to cause se­vere gum disease. More than 60% of bacteria in the human mouth refuse to grow in a laboratory dish, which means they have never been classified, named, or studied. The newly sequenced bacterium, Tan­nerella BU063, is among those that to date have not successfully been grown in culture—and its genome is identified as “most wanted” by the Human Microbiome Project.

Those 12 cells of BU063 are a good example of the complexity of life in the mouth: They came from a single healthy person but represented 8 different strains of the bacterium. BU063 is closely related to the pathogen Tannerella forsythia, a bacterium linked to periodontitis, but the 2 have clear differences in their genetic makeup. Those genes lacking in BU063 but present in T forsythia are likely a secret behind T forsythia’s virulence and are good targets for further study. There is one particular gene complex in a whole list of periodontitis-related bacteria that could be involved with virulence.

Completing the genome of BU063 was a feat in itself, but the larger purpose was learning more about T forsythia; the reason behind its virulence hasn’t been confirmed. This research supported an existing theory that 3 genes could be related to T forsythia’s ability to cause disease because these genes are missing from BU063. Two have potential to damage tissue and inactivate the immune response and the third is a cell-surface molecule that interacts with human cells. The research is published in the journal PLOS ONE.

(Source: Ohio State Uni­versity. “Scientists chip away at mystery of what lives in our mouths.” ScienceDaily. February 14, 2014)