Robust variation in infant gut microbiome assembly across a spectrum of lifestyles

Infant microbiome assembly has been intensely studied in infants from industrialized nations, but little is known about this process in nonindustrialized populations. We deeply sequenced infant stool samples from the Hadza hunter-gatherers of Tanzania and analyzed them in a global meta-analysis. Infant microbiomes develop along lifestyle-associated trajectories, with more than 20% of genomes detected in the Hadza infant gut representing novel species. Industrialized infants-even those who are breastfedhave microbiomes characterized by a paucity of Bifidobacterium infantis and gene cassettes involved in human milk utilization. Strains within lifestyle-associated taxonomic groups are shared between motherinfant dyads, consistent with early life inheritance of lifestyle-shaped microbiomes. The populationspecific differences in infant microbiome composition and function underscore the importance of studying microbiomes from people outside of wealthy, industrialized nations.