Researchers from UCL in the United Kingdom have discovered that the mix of microorganisms in a person’s saliva are largely determined by the household they live in. The study showed that early environmental influences play a far larger role than human genetics in shaping the salivary microbiome. The microbiome are organisms that play an important role in oral and overall health. The oral cavity is colonized by hundreds of bacterial species, which stop external pathogens but they also can cause oral disease. The researchers were interested in exploring how the salivary microbiome becomes established and which factors are most responsible.
The researchers used DNA and saliva from an extended Ashkenazi Jewish family living in various households spread across four cities on three continents. The family members are believed to have shared cultural diets and lifestyles that control for many confounding factors. The DNA had already been sequenced to the level of single changes in the DNA code which provided insights into their genetic relatedness. The researchers also sequenced the DNA present in saliva samples from 157 family members and 27 unrelated Ashkenazi Jewish controls. They found the core salivary microbiome made up of bacteria from the genera Rothia, Neisseria, Streptococcus, and Prevotella.
The researchers used statistical methods to determine which factors are responsible for the most variation. When comparing factors such as city, age, household, and genetic relatedness, the factor that determined who shared the most similar saliva microbes was household. Spouses and parents and children younger than 10 living in a household together had the most similar saliva microbiomes. The researchers believe that contact played a role but it did not have to be intimate. Children younger than 10 were found to have more similar bacteria to their parents than to their older siblings.
The researchers also explored whether genetic relatedness drove the makeup of the saliva microbiome. They used a measure of relatedness based on family tree relationships alone and saw a small, statistically significant effect. When they looked at the genetic sequence information the effect disappeared. Essentially this means that a person’s genetics played almost no role in shaping their saliva microbes. This study shows shared environments play a major role in determining what bacteria becomes established. The researchers feel that knowing that the environment drives the microbiome may one day allow for behavior to shift which can lead to a more favorable microbiome. It is known that periodontitis (gum disease) is associated with an altered microbiome. So potentially making subtle changes in the environment you live in may affect if you develop periodontitis or not at a later age.
Source: Liam Shaw and et. al., The Human Salivary Microbiome Is Shaped by Shared Environment Rather than Genetics: Evidence from a Large Family of Closely Related Individuals, mBio, vol. 8, issue 5, 2017.