What is already known
Studies have shown that people living in industrialized countries tend to have a less diverse microbiota than people from nonindustrial populations. But whereas the assembly of the infant microbiota has been studied in children from industrialized nations, little is known about this process in nonindustrial populations, and how it contributes to the differences in adult microbiota composition.
What this research adds
Researchers analyzed infant stool samples from the Hadza people, a group of modern hunter-gatherers living in Tanzania, and compared the data with fecal sample records from infants from 17 industrialized populations. The team found that after the first 6 months of life, the microbiota of infants living in industrialized countries had low levels of Bifidobacterium infantis, a bacterium that is able to use human milk oligosaccharides and is commonly given as a probiotic supplement. More than 20% of the bacterial species detected in samples from Hadza children were novel, and many of these were undetectable in samples from children from industrialized areas. The team also found that microbes associated with nonindustrial lifestyles were shared between mothers and their infants.
Conclusions
The findings suggest that gut microbiota diversity appears early in infants from nonindustrial populations and could be traced back to their mothers as well as to the local environment.
People living in industrialized countries tend to have a less diverse microbiota than people from nonindustrial populations. New research shows that microbiota diversity appears early in infants from nonindustrial populations and could be traced back to their mothers as well as to the local environment.
The findings, published in Science, suggest that lifestyle rather than geography is the main driver for differences in gut microbiota. The results also “underscore the importance of studying microbiomes from people outside of wealthy, industrialized nations,” the researchers say.
The assembly of the infant microbiota has been studied in children from industrialized nations, but little is known about this process in nonindustrial populations, and how it contributes to the differences in adult microbiota composition.
To fill this knowledge gap, Justin Sonnenburg at Stanford University and his colleagues set out to collect stool samples from infants of the Hadza people, a group of modern hunter-gatherers living in Tanzania. “The Hadza inhabit seminomadic bush camps of ~5 to 30 people, exhibit a moderate level of community child rearing within these camps, and are breastfed early in life and weaned onto a diet of baobab powder and pre-masticated meat at ~2 to 3 years of age,” the authors say.
Microbiota differences
The researchers analyzed 62 infant stool samples from the Hadza people, and then compared the data with fecal sample records from infants from 17 industrialized populations.
Bifidobacterium and Streptococcus bacteria tended to dominate the infant gut from all populations from 0 to 6 months of age. In the first 6 months, the guts of infants living nonindustrial lifestyles were dominated by Bifidobacterium infantis, a bacterium that is able to use human milk oligosaccharides and is commonly given as a probiotic supplement. Instead, the levels of B. infantis were low in the microbiota of infants from industrial environments.
Bifidobacterium breve, a species with limited ability to use human milk oligosaccharides, was the most abundant Bifidobacterium species in industrialized infants. These infants — even those who were breastfed — also showed lower levels of microbial genes involved in human milk utilization.
Compared to infants living in industrialized areas, Hadza infants had more diversity in their guts after about 6 months. More than 20% of the bacterial species detected in samples from Hadza children were novel, and many of these were undetectable in samples from children from industrialized areas.
Mother-to-infant transmission
To assess how much of the microbiota is transmitted from mothers to infants, the team sequenced fecal samples from 23 Hadza mothers and their infants.
Hadza mothers tended to transmit Bacteroidota and Cyanobacteria, but not Firmicutes. Similar patterns were observed in infants from industrialized areas. “These results suggest that community interaction during rearing of infants and/or bush camp microenvironments may propagate group microbial sharing,” the researchers say.
The researchers also found that Prevotella bacteria, which are enriched in non-industrialized infants, were more commonly transmitted from Hadza mothers to their infants, whereas Bacteroides, which are enriched in industrialized infants, were more commonly transmitted from mothers to their infants in industrialized countries such as Sweden.
The findings suggest that the transmission of specific gut microbes may be a mechanism by which microbiota change is propagated over generations in response to lifestyle, the researchers say. The results, they add, “also highlight the question of whether lifestyle-specific differences in the gut microbiome’s developmental trajectory predispose populations to diseases common in the industrialized world, such as those driven by chronic inflammation.”
