Your roommate’s genes may be shaping your gut bacteria
Scientists studying thousands of rats discovered that gut bacteria are shaped by both personal genetics and the genetics of social partners. Some genes promote certain microbes that can spread between individuals living together. When researchers accounted for this social sharing, genetic influence on the microbiome turned out to be much stronger than previously thought. The study suggests genes can affect others indirectly, without DNA ever being exchanged.
The genes of your roommate may be shaping the bacteria in your gut, and your genes may be influencing theirs, according to a rat study published on December 18 in Nature Communications.
By examining more than four thousand rats, researchers found that the makeup of the gut microbiome is affected not only by an individual's own genetic makeup but also by the genes of the animals they share their living space with.
The findings point to a new way genetics and social interactions are connected. Certain commensal gut microbes can move between individuals through close contact. While genes themselves stay put, microbes do not. The study showed that some genes promote the growth of specific gut bacteria, and those bacteria can spread socially.
"This is not magic, but rather the result of genetic influences spilling over to others through social contact. Genes shape the gut microbiome and we found that it is not just our own genes that matter," says Dr. Amelie Baud, a researcher at the Centre for Genomic Regulation in Barcelona and senior author of the study.
Three new gene microbe links identified in rats
The gut microbiome consists of trillions of microorganisms living in the digestive tract, where they play important roles in digestion and overall health. Diet and medications are known to strongly influence these microbial communities, but understanding how genetics contributes has been far more challenging.
In humans, researchers have reliably linked only two genes to gut bacteria. The lactase gene determines whether adults can digest milk and affects milk digesting microbes. The ABO blood group gene also influences gut bacteria, though the exact mechanisms remain unclear.
Scientists believe additional gene microbe links likely exist, but proving them is difficult because genetic and environmental factors overlap in everyday life. Genes can shape diet and lifestyle choices, which then influence the gut microbiome. At the same time, families and friends often share food, living spaces, and microbes, making it hard to separate nature from nurture.
To overcome these challenges, researchers at the Centre for Genomic Regulation and the University of California San Diego turned to rats. Rats share many key aspects of mammalian biology and can be raised under tightly controlled conditions, including identical diets.
Each rat in the study was genetically unique and belonged to one of four separate cohorts. These cohorts were housed at different facilities across the United States and followed different care routines, allowing researchers to test whether genetic effects remained consistent across environments.
By combining genetic data with microbiome profiles from all 4,000 rats, the team identified three genetic regions that consistently influenced gut bacteria across all four cohorts.
The strongest association involved the gene St6galnac1, which adds sugar molecules to the mucus lining of the gut. This gene was linked to higher levels of , a bacterium believed to feed on these sugars. This connection appeared in every cohort.