Nurture wins out over nature in mouth’s bacterial world

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Washington, October 12: A new long-term study of human twins has indicated that the makeup of the population of bacteria bathing in their saliva is driven more by environmental factors than heritability.

The study by University of Colorado Boulder researchers compares 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 and CU-Boulder Professor Kenneth Krauter.

The twin studies show that the environment, rather than a person’s genetic background, is more important in determining the types of microbes that live in the mouth.

For the new study, doctoral student Simone Stahringer sequenced the microbial DNA present in the saliva samples of twins. She and the research team then 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,” Krauter said.

“It appears to be more of an environmental effect,” Krauter said.

Krauter said while the twin data from the oral microbiome study indicates that genetics plays a more minor role, it’s possible the genes still affect the oral microbiome in more subtle ways-an effect he plans to further explore.

The researchers 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.

Stahringer 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,” Stahringer said.

Krauter said there appears to be a core community of oral bacteria that is present in nearly all humans studied.

“Though there are definitely differences among different people, there is a relatively high degree of sharing similar microbial species in all human mouths,” he added.

The study has been recently published online in Genome Research. (ANI)