Household environment—not genetics—shapes salivary microbes

September 12, 2017

Researchers in the United Kingdom have discovered that the mix of microorganisms that inhabit a person's saliva are largely determined by the human host's household. The study, published this week in mBio, an open-access journal of the American Society for Microbiology, shows that early environmental influences play a far larger role than human genetics in shaping the salivary microbiome—the group of organisms that play a crucial role in oral and overall health.

"It's generally becoming known that there's a link between our microbiomes and our health and that's reason enough to find out what's in there, how they arrived there, and what they are doing," says Adam P. Roberts, senior lecturer in antimicrobial chemotherapy and resistance at the Liverpool School of Tropical Medicine. Roberts co-led the study, which was conducted during his previous post at the UCL Eastman Dental Institute. UCL Genetics Institute graduate student Liam Shaw adds, "The oral cavity is naturally colonized by hundreds of , which stop external pathogens from establishing a foothold, but they also can themselves cause oral disease."

The research team wanted to know how the salivary gets established and which factors are most responsible for the mix of bacteria found there. Roberts' colleague, UCL immunologist Andrew M. Smith, had access to a unique sample set—DNA and from an extended, Ashkenazi Jewish family living in various households spread across four cities on three continents. That allowed the team ask how much of the variation seen in salivary microbiomes is due to host genetics and how much is due to environment.

Because the are ultra-orthodox Ashkenazi Jews, they share cultural diets and lifestyles that control for many confounding factors. Also, because the family members' DNA had already been sequenced to the level of single changes in the DNA code, the research team had a unique and precise measurement of their genetic relatedness.

Next, Shaw and the team sequenced the bacterial DNA signatures present in saliva samples from 157 family members and 27 unrelated Ashkenazi Jewish controls. Across all samples, they found the core salivary microbiome made up of bacteria from the genera Streptococcus, Rothia, Neisseria, and Prevotella.

To get at what might be driving differences at the bacterial species level, Shaw and the team used statistical methods adopted from ecology to determine which factors are responsible for the most variation. When comparing factors such as shared household, city, age, and genetic relatedness, the factor that determined who shared the most similar saliva microbes was overwhelmingly household.

"What that tells us is that the contact and sharing of microbes that goes on at the very local environment is what determines the differences between individuals," says Shaw.

Spouses and parents and children younger than 10 living in a household together had the most similar saliva microbiomes. "The contact doesn't even have to be intimate, like kissing," says Roberts. "Individuals' hands are covered in saliva and they are touching everything in the house." Children younger than 10 had more similar bacteria to their parents than older children, perhaps reflecting that older children are becoming "more independent individuals," says Roberts.

The team also looked carefully at whether genetic relatedness drove the makeup of the saliva microbiome. When they used a measure of relatedness based on family tree relationships alone, they saw a small, but statistically significant effect. However, when they used the genetic sequence information, a more accurate measure of relatedness, the effect disappeared. In other words, a person's genetics played virtually no role in shaping their saliva microbes.

"Pedigrees do not always precisely reflect actual in terms of the amount of genome shared," says Shaw. Roberts encourages other researchers undertaking large-scale microbiome studies to use detailed human genetic sequence information rather than relying on family trees.

This study shows that environments shared during upbringing play a major role in determining what community of bacteria gets established. And knowing that the shared environment drives the microbiome, Roberts says, may gives us the ability to one day modulate it.

He points to the example of periodontitis, or gum disease, an incredibly common and often debilitating infectious disease associated with an altered microbiome. "Once we understand the members of the microbiome that are responsible for health, our everyday behavior could change to shift our microbiome favorably."

Explore further: Study links changes in oral microbiome with metabolic disease

Related Stories

Study links changes in oral microbiome with metabolic disease

March 1, 2017
A team of scientists from The Forsyth Institute and the Dasman Diabetes Institute in Kuwait have found that metabolic diseases, which are characterized by high blood pressure, high blood sugar, and obesity—leads to changes ...

Nurture trumps nature in study of oral bacteria in human twins

October 11, 2012
A new long-term study of human twins by University of Colorado Boulder researchers indicates the makeup of the population of bacteria bathing in their saliva is driven more by environmental factors than heritability.

Recommended for you

Genome editing reveals role of gene important for human embryo development

September 20, 2017
Researchers have used genome editing technology to reveal the role of a key gene in human embryos in the first few days of development. This is the first time that genome editing has been used to study gene function in human ...

A piece of the puzzle: Eight autism-related mutations in one gene

September 19, 2017
Scientists have identified a hotspot for autism-related mutations in a single gene.

Scientists identify key regulator of male fertility

September 19, 2017
When it comes to male reproductive fertility, timing is everything. Now scientists are finding new details on how disruption of this timing may contribute to male infertility or congenital illness.

New assay leads to step toward gene therapy for deaf patients

September 18, 2017
Scientists at Oregon State University have taken an important step toward gene therapy for deaf patients by developing a way to better study a large protein essential for hearing and finding a truncated version of it.

Biologists identify gene involved in kidney-related birth defects

September 18, 2017
A team led by University of Iowa researchers has identified a gene linked to rare, often fatal kidney-related birth defects.

Genomic recycling: Ancestral genes take on new roles

September 18, 2017
One often hears about the multitude of genes we have in common with chimps, birds or other living creatures, but such comparisons are sometimes misleading. The shared percentage usually refers only to genes that encode instructions ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.