Gut microbial communities shaped by human genetic factors
A collaborative research group studying a large population of twins in the United Kingdom has shown that human genetic factors shape the composition of the gut microbial community, and some gut microbes may in turn affect the metabolism of their human “hosts.” The first members of the gut microbiome, the collection of all microbes present in the gut and/or their genetic material, are acquired from the maternal “environment” at birth, or possibly even earlier in the womb. Similar gut microbiomes in related adults are often attributed largely to a shared environment, including common diets. However, previous studies also hinted at the possibility that other determinants of an individual’s unique gut microbiome over time may lie in one’s own human genome. Researchers based at institutions in the United States and the United Kingdom set out to analyze a sufficiently large number of people to test this idea, using the TwinsUK study. They collected fecal samples from 416 pairs of identical or fraternal twins. By sequencing a portion of the microbial genetic material from each of those samples, they were able to identify and quantify specific gut microbial species present in the twins’ samples. Pairs of genetically identical twins had more similar gut microbiomes than pairs of fraternal twins did. Within the identical twin pairs, winning the prize for the group of gut microbes whose abundance was most closely tied to human genetic influences were members of the Christensenallaceae family—a family of bacteria that has only been described since 2012. The varying abundance of these bacteria in different twin pairs may actually have a larger impact on their gut microbial communities, as they tended to coincide with certain other gut microbes. The researchers also noticed that the Christensenallaceae family microbes were more abundant in lean study participants than in those who were obese. They tested whether these microbes might protect against weight gain by introducing microbes from obese participants into mice that had been raised up to that point in a sterile environment (free of microbes). To some of the mice they also introduced bacteria from one species of Christensenallaceae. After 3 weeks, the mice that received Christensenallaceae family microbes along with the obese donor’s gut microbes were leaner than those that received only the obese donor’s microbes. These findings point to members of this microbial family as important contributors to human metabolism, with potential effects on weight gain, and show that its abundance, and in some cases presence or absence, is strongly affected by one’s genes. This may be one way in which genes affect human metabolic health: by influencing the capacity to host beneficial microorganisms. Future studies will explore which human genes influence the components of the gut microbiome. Such knowledge could inform future health-promoting interventions, potentially suggesting ways to adjust gut microbial levels depending on an individual’s genetic background.