Microbial communities in placentas from term normal pregnancy exhibit spatially variable profiles

Abstract

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.

Impact of pregravid obesity on maternal and fetal immunity: Fertile grounds for reprogramming

“…In addition to immune cells, the placenta harbors a low abundance but metabolically rich microbiome 147 that varies from the decidua to basal plates to the fetal membranes. 148 This microbial community is disrupted with preterm labor, 149 PE 150 and gestational weight gain, 151 and pregravid obesity. 126 Some of these studies were carried out using placenta samples of preterm births; therefore, our understanding of the impact of pregravid obesity on microbial communities within the term placental decidua remains limited.…”

“…In addition to immune cells, the placenta harbors a low abundance but metabolically rich microbiome that varies from the decidua to basal plates to the fetal membranes . This microbial community is disrupted with preterm labor, PE and gestational weight gain, and pregravid obesity .…”

Functional characterization ofRalstonia insidiosa, a bona fide resident at the maternal-fetal interface

“…We found a high prevalence of R. insidiosa, a waterborne environmental bacterium, in human BPs using multi-variable region 16S sequencing approach 19 . Other investigators have also identified Ralstonia spp.…”

“…Whether there are microbiota (live or simply DNA signatures) in the maternal-fetal interface remains mired in controversy. In the recent years, there has been a large number of studies, providing both sequencing and histological evidence, indicating microbial signatures 3,11,18,19,22,23,29 , while other studies have reported these signatures as likely DNA contaminants originating from the sample collection and/or the DNA extraction process, rather than the placenta itself [54][55][56][57] . Placenta location remains a key variable in the aforementioned studies given that that BP, PV and FM have distinct physiology and function.…”

“…We found that Ralstonia insidiosa (R. insidiosa), a gram-negative, aerobic, motile bacillus, is most prevalent in the BP 19 . R. insidiosa was first isolated from the sputum of cystic fibrosis patients and can be isolated from immunocompromised patients in hospitals 31,32 .…”