The gut bacteria profile of the Tanzanian Hadza people display annual seasonal variations, with the changes following their varying seasonal dietary patterns, found the study team led by Stanford University.
The cyclical pattern showed that the hunter-gatherers’ microbiomes reconfigured annually, with numbers of certain bacterial types becoming undetectable and subsequently reappearing the following season. Numbers of Bacteroidetes, a major bacterial phylum declined by around 70% between the end of the dry season and the start of the wet season, only to reappear later. The Hadza’s dietary pattern is subject to two distinct seasons, wet and dry.
The results were logical, suggested co-lead author Professor Justin Sonnenburg.
"Our own microbiota can change significantly from day to day, or even within hours, in response to what we've been eating," he commented.
The researchers also found greater microbial diversity in the Hazda microbiome than in urban industrialised populations. They hypothesised that dramatic changes to the human diet over thousands of years could explain this loss of diversity within the modern human gut.
During the seasonal disappearance of certain species “the Hadza microbiota shifts to a state with increased similarity to those of industrialised microbiotas,” explained Sonnenburg.
"Surviving hunter-gatherer populations are the closest available proxy to a time machine we in the modern industrialised world can climb into to learn about the ways of our remote human ancestors," he continued.
The researchers collected 350 faecal samples from 188 members of the Hadza community across the different seasons over a year, thereby incorporating variations in diet.
They subsequently compared the Hadza’s microbiome composition with those of 18 populations from 16 different countries, reflecting a mixture of ‘traditional’ African, Asian and South American communities (ranging from hunter-gatherers to rural agriculturalists), as well as industrialised communities.
“Industrialised populations had microbiotas dominated by Bacteroidaceae (mean 20.9% versus 0.8% in traditional,” wrote the researchers.
By contrast, traditional populations displayed an abundance of Prevotellaceae – 29.8%, versus 7.6% in industrialised nations.
Additionally, the Hadza displayed bacterial profiles that were more capable of processing plant carbohydrates than Americans consuming a western diet. The gut genomes of the hunter-gatherers also contained far fewer antibiotic-resistant genes than those of their industrialised counterparts.
The researchers found that two bacterial families, Spirochaetaceae and Succinivibrionaceae, prevalent in the Hadza and other traditional communities, were rare or undetected in the guts of industrialised populations.
“These data indicate that some dynamic lineages of microbes have decreased in prevalence and abundance in modernized populations,” suggested the researchers.
An earlier study in mice, led by Sonnenburg had suggested that absence of dietary fibre reduced microbiota diversity, which was resored by reintroduction of fibre intake. Nevertheless, if fibre deprivation continued for four generations certain species were permanently lost and not restored.
If the same pattern is applicable in humans, this may explain the decline in human gut microbial diversity over multiple generations.
"The 100 to 200 Hadza sticking to this routine will possibly lose it in a decade or two, maybe sooner. Some are using cell phones now," Sonnenburg said. "We wanted to take advantage of this rapidly closing window to explore our vanishing microbiota."
Further research into the microbiome in the Hazda was previously covered by NutraIngredients, and can be read here .
Vol. 357, Issue 6353, pp. 802-806, doi 10.1126/science.aan4834
“Seasonal cycling in the gut microbiome of the Hadza hunter-gatherers of Tanzania”
Authors: Samuel A. Smits, Jeff Leach, Justin L. Sonnenburg et al.