A new long-term study of human twins by University of Colorado Boulder researchers indicated the makeup of the population of bacteria in their saliva is driven more by environmental factors than heritability.
"The study compared saliva samples from identical and fraternal twins to see how much "bacterial communities" in saliva vary from mouth to mouth at different points in time," said study leader Professor Kenneth Krauter.
Researchers sequenced the microbial DNA present in the saliva samples of twins and determined the microbes' identities through comparison with a microbe sequence database.
Saliva samples were gathered from twins over the course of a decade beginning in adolescence to see how salivary microbes change with time.
After determining the oral "microbiomes" of identical twins, who share the same environment and genes, and the microbiomes of fraternal twins who share only half their genes, the researchers found the salivary microbes of the identical twins were not significantly more similar to each other than to those of fraternal twins.
"We concluded the human genome does not significantly affect which bacteria are living in a person's mouth. It appears to be more of an environmental effect," said Krauter.
The study also found that the salivary microbiome changed the most during early adolescence, between the ages of 12 and 17. This discovery suggests that hormones or lifestyle changes at this age might be important, according to the team.
Researchers said that when several pairs of identical twins moved out of their homes and, for example, went off to college, the oral microbes they carried changed, which is consistent with the idea that the environment contributes to the types of microbes in the saliva.
"We were intrigued to see that the microbiota of twin pairs became less similar once they moved apart from each other," researcher Simone Stahringer said.
The study was published in the journal Genome Research.
