PROFILE OF TERM PLACENTAL MICROBIAL TRANSCRIPTOME

The existence of various microbial DNA in human placental samples was described by Aagaard et al. (2014) using 16S rDNA and whole genome analyses. However, the DNA-based approach does not distinguish between living and dead bacteria. We aimed to characterize the abundance of living bacteria hosting the human placenta by utilizing the analysis of unmapped reads of placental RNA-Seq data from clinically well described cases over a range of term pregnancy outcomes. Methodology. Microbial profile of previously established RNA-Seq data of 40 placental samples taken at delivery (Sober et al. 2015) was identified using MEGABLAST. Matches with highest bitscore for each read were recorded. Results. Subsequently, over 7.3 Gbp filtered non-human reads were analysed. Placental microbial transcriptome revealed three major bacterial phyla: Proteobacteria (60%), Actinobacteria (24%) and Firmicutes (16%). Consistent with the study based on 16S rDNA (Aagaard et al. 2014), the most prevalent single species present in every placental sample was Escherichia coli. Altogether 48 strains were identified. Conclusion. In conclusion, our data robustly demonstrates that placenta is a natural habitat for living bacteria (mainly for Proteobacteria). Although the prevalence of other bacterial phyla in term placentas appears to be moderate, their role is still to be investigated.