Phylum level differences in the gut bacteria of nursing infants and growth-related decreases in iron reserves are associated with myelin microstructure in cortical white matter tracts in rhesus monkeys

: This research investigated two maternal processes that affect neurodevelopment: 1) the prenatal endowment of maternal iron that supports growth-related iron needs, and 2) exposure to maternal bacteria and breast milk that shape the postnatal assemblage of the infant’s gut microbiota. A primary aim was to extend prior results indicating that the bacterial profile of nursing infant monkeys is normally dominated by a high abundance of Bifidobacteria (Phylum Actinomycetota), and that the presence of higher abundance of taxa in the Phylum Pseudomonadota provides a sentinel indicator of slower brain maturation. This perspective was applied to additional infants who became anemic subsequently at end of the nursing period. Fecal and blood specimens were collected from 41 infant rhesus monkeys; diffusion tensor imaging scans were acquired at one year of age. Axial-based fiber tract analyses examined fractional anisotropy (FA) values in three major myelinated projections: the cingulum (CG), uncinate fascicularis (UF), and inferior longitudinal fascicularis (ILF). Fecal samples were collected from nursing infants at 2 months postpartum, prior to the onset of infantile anemia, and analyzed with 16S ribosomal RNA gene amplicon sequencing. The analysis focused on the 4 most abundant phyla. Pseudomonadota were inversely associated with FA in the cingulum tract. Sixteen of the 41 infants subsequently became iron deficient between 4-8 months of age and there was an overall trend for a negative influence on FA values. The findings convey that both gut bacterial profiles and iron status during infancy may influence the myelination of important tracts connecting the temporal lobe with other cortical areas.