Owing to the fact that there are more microbial than human cells in our body and that humans contain more microbial than human genes, the microbiome has huge potential to influence human physiology, both in health and in disease.
The use of next-generation sequencing technologies has helped to elucidate functional, quantitative and mechanistic aspects of the complex microorganism'host interactions that underlie human physiology and pathophysiology.
The microbiome of semen is a field of increasing scientific interest, although this microbial niche is currently understudied compared with other areas of microbiome research. However, emerging evidence is beginning to indicate that the seminal microbiome has important implications for the reproductive health of men, the health of the couple and even the health of offspring, owing to transfer of microorganisms to the partner and offspring.
- As this field expands, further carefully designed and well-powered studies are required to unravel the true nature and role of the seminal microbiome.
- Semen has a unique microbiome; however, its origin and function need to be further investigated in order to understand its role in health and disease.
- Alterations in the bacterial composition of semen have been linked to a variety of disorders, including subinfertility and poor semen quality, prostatitis and HIV infection.
- The seminal microbiome might influence a couple's health and even that of their offspring, as well as affecting pregnancy outcomes.
- When studying the male seminal microbiome, the partner's reproductive tract microbiome and the sexual behaviours of both partners should also be considered.
- Study of the seminal microbiome is still in its infancy, and further well-designed, large-cohort, functional studies are required.
1. Power, M. L., Quaglieri, C. & Schulkin, J. Reproductive microbiomes. Reprod. Sci. 24, 1482'1492 (2017).
2. Sender, R., Fuchs, S. & Milo, R. Are we really vastly outnumbered' Revisiting the ratio of bacterial to host cells in humans. Cell 164, 337'340 (2016).
3. Sender, R., Fuchs, S. & Milo, R. Revised estimates for the number of human and bacteria cells in the body. PLOS Biol. 14, e1002533 (2016).
4. Grice, E. A. & Segre, J. A. The human microbiome: our second genome. Annu. Rev. Genomics Hum. Genet. 13, 151'170 (2012).
5. Wang, B., Yao, M., Lv, L., Ling, Z. & Li, L. The human microbiota in health and disease. Engineering 3, 71'82 (2017).
6. Kroon, S. J., Ravel, J. & Huston, W. M. Cervicovaginal microbiota, women's health, and reproductive outcomes. Fertil. Steril. 110, 327'336 (2018).
7. Benner, M., Ferwerda, G., Joosten, I. & van der Molen, R. G. How uterine microbiota might be responsible for a receptive, fertile endometrium. Hum. Reprod. Update 24, 393'415 (2018).
8. Baker, J. M., Chase, D. M. & Herbst-Kralovetz, M. M. Uterine microbiota: residents, tourists, or invaders' Front. Immunol. 9, 208 (2018).
9. Altmäe, S. Commentary: uterine microbiota: residents, tourists, or invaders' Front. Immunol. 9, 1874 (2018).
10. Franasiak, J. M. & Scott, R. T. Endometrial microbiome. Curr. Opin. Obstet. Gynecol. 29, 146'152 (2017).
11. Moreno, I. & Franasiak, J. M. Endometrial microbiota-new player in town. Fertil. Steril. 108, 32'39 (2017).
12. Moreno, I. et al. Evidence that the endometrial microbiota has an effect on implantation success or failure. Am. J. Obstet. Gynecol. 215, 684'703 (2016).
13 . Altmäe, S. Uterine microbiota: a role beyond infection. EMJ Reprod. Heal. 6, 70'75 (2018).
14. Franasiak, J. M. & Scott, R. T. Reproductive tract microbiome in assisted reproductive technologies. Fertil. Steril. 104, 1364'1371 (2015).
15.Nguyen, P. V., Kafka, J. K., Ferreira, V. H., Roth, K. & Kaushic, C. Innate and adaptive immune responses in male and female reproductive tracts in homeostasis and following HIV infection. Cell. Mol. Immunol. 11, 410'427 (2014).
16. Weng, S. L. et al. Bacterial communities in semen from men of infertile couples: metagenomic sequencing reveals relationships of seminal microbiota to semen quality. PLOS ONE 9, e110152 (2014).
17. Chen, H., Luo, T., Chen, T. & Wang, G. Seminal bacterial composition in patients with obstructive and non'obstructive azoospermia. Exp. Ther. Med. 15, 2884'2890 (2018).
18. Monteiro, C. et al. Characterization of microbiota in male infertility cases uncovers differences in seminal hyperviscosity and oligoasthe