A descriptive analysis of gut microbiota composition in differentially reared infant rhesus monkeys ( Macaca mulatta ) across the first 6 months of life

: The gastrointestinal microbiome is recognized as a critical component in host immune function, physiology, and behavior. Early life experiences that alter diet and social contact also influence these outcomes. Despite the growing number of studies in this area, no studies to date have examined the contribution of early life experiences on the gut microbiome in infants across development. Such studies are important for understanding the biological and environmental factors that contribute to optimal gut microbial colonization and subsequent health. We studied infant rhesus monkeys (Macaca mulatta) across the first 6 months of life that were pseudo-randomly assigned to one of two different rearing conditions at birth: mother-peer-reared (MPR), in which infants were reared in social groups with many other adults and peers and nursed on their mothers, or nursery-reared (NR), in which infants were reared by human caregivers, fed formula, and given daily social contact with peers. We analyzed the microbiome from rectal swabs (total N = 97; MPR = 43, NR = 54) taken on the day of birth and at postnatal Days 14, 30, 90, and 180 using 16S rRNA gene sequencing. Bacterial composition differences were evident as early as 14 days, with MPR infants exhibiting a lower abundance of Bifidobacterium and a higher abundance of Bacteroides than NR infants. The most marked differences were observed at 90 days, when Bifidobacterium, Lactobacillus, Streptococcus, Bacteroides, Clostridium, and Prevotella differed across rearing groups. By Day 180, no differences in the relative abundances of the bacteria of interest were observed. These novel findings in developing primate neonates indicate that the early social environment as well as diet influence gut microbiota composition very early in life. These results also lay the groundwork for mechanistic studies examining the effects of early experiences on gut microbiota across development with the ultimate goal of understanding the clinical significance of developmental changes.