Intestinal microflora is a complex system that affects immunity, metabolism, and even mood. Until recently, it was assumed that diet and lifestyle primarily shape it. A new study showed that the microbiome is also influenced by a person’s own genes and the genes of those with whom they reside.
Scientists had long suspected that genes influence gut bacteria. For instance, the lactase gene determines whether an adult can digest milk. If it is active, there are more bacteria in the gut that process lactose. Another illustration is the ABO blood type gene, which is also linked to certain kinds of microbes. However, only a few such proven connections existed.
The challenge is that with humans, it is very difficult to separate the influence of genes from the impact of the environment. People with similar genes often live together, consume the same food, and exchange microbes. Therefore, discerning what precisely affects the microbiome—genes or lifestyle—is tricky.
The work is published in Nature Communications. Researchers from the Center for Genomic Regulation and the University of California San Diego conducted an experiment on rats. They took four thousand rodents, each of which was genetically unique. The animals were divided into four cohorts and kept in different laboratories across the United States. In each lab, the rats lived in identical surroundings and ate the same sustenance—this allowed them to rule out the impact of diet and setting.
The scientists pinpointed three DNA regions that consistently affected the composition of the microflora across all groups. The strongest association was with the ST6GALNAC1 gene, which appends sugar molecules to the intestinal lining. This gene was associated with the bacterium Paraprevotella, which consumes these sugars. Other genes linked to mucin (the substance forming the mucous layer) impacted bacteria from the Firmicutes group. The third gene, PIP, which is responsible for producing antibacterial agents, related to bacteria of the Muribaculaceae family.
The scientists observed that the abundance of specific bacteria was shaped not just by the rat’s own genes but also by the genes of the rodents with whom it lived. This implies that genes can project their effect through microbes transmitted from one animal to another.
When the researchers factored in this “social effect” in their calculations, it emerged that the total genetic impact on the microbiome amplified by four to eight times. This suggests that genetics’ role in shaping microflora has been greatly underestimated.
Although the trial was conducted on rats, the findings might elucidate how these mechanisms operate in humans. We, too, continuously exchange microbes with those we live alongside.
This discovery could clarify why some individuals fall ill more frequently than others, even if they share a similar way of life. For example, genes influencing microflora composition might alter the risk of developing infections or autoimmune conditions. If a relative has genes promoting the growth of certain bacteria, those genes could transfer to you and alter your microbiome.
In the future, this finding may enable the creation of novel methods for disease prevention and treatment. For instance, if which genes impact the microbiome becomes known, it will be possible to select probiotics or diets more precisely. Or even to devise medicines that will modify the microflora via genetic pathways.
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