The placenta is the principal organ nurturing the fetus during pregnancy and was traditionally considered to be sterile. Recent work has suggested that the placenta harbours microbial communities, however the location and possible function of these microbes remain to be confirmed and elucidated. Here, we employed genomic DNA sequencing of multiple variable (V) regions of the bacterial 16S ribosomal gene, to interrogate microbial profiles in term pregnancies, from the basal plate, which is in direct contact with maternal uterine, endothelial, and immune cells; placental villi, which are bathed in maternal blood, and fetal membranes, which encapsulate the amniotic cavity. QIIME, R package “Phyloseq” analysis was used to assess alpha and beta diversity and absolute abundance of the 16S rRNA gene per location. We demonstrate that (1) microbiota exhibit spatially distinct profiles depending on the location within the placenta and (2) “semi-composite” 16S profiles using multiple V regions validated by quantitative PCR analysis confirmed that distinct bacterial taxa dominate in different placental niches. Finally, profiles are not altered by mode of delivery. Together these findings suggest that there is niche-specificity to the placental microbiota and placental microbiome studies should consider regional differences, which may affect maternal, fetal, and/or neonatal health and physiology.

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Significance Dietary fibers contain complex mixtures of biomolecules, making it difficult to develop/test hypotheses about how different fiber-types impact different components of the human gut microbiome and how microbiome changes that they produce are linked to human physiology. Here, we analyze microbiome and plasma proteome responses to consumption of two fiber-enriched snacks in two human studies. We use a variety of computational methods to correlate their effects on gut microbiome genes encoding enzymes that degrade complex fiber-associated polysaccharides, the microbial products of polysaccharide degradation, and plasma proteins representing diverse physiological processes. This approach can be used to guide the design of fiber-containing snacks that more precisely manipulate microbiome features in ways that improve nutritional and health status.