Assessing the testicular sperm microbiome: a low-biomass site with abundant contamination.

RESEARCH QUESTION:The semen harbours a diverse range of microorganisms. The origin of the seminal microbes, however, has not yet been established. Do testicular spermatozoa harbour microbes and could they potentially contribute to the seminal microbiome composition? DESIGN:The study included 24 samples, comprising a total of 307 testicular maturing spermatozoa. A high-throughput sequencing method targeting V3 and V4 regions of 16S rRNA gene was applied. A series of negative controls together with stringent in-silico decontamination methods were analysed. RESULTS:Between 50 and 70% of all the detected bacterial reads accounted for contamination in the testicular sperm samples. After stringent decontamination, Blautia (P = 0.04), Cellulosibacter (P = 0.02), Clostridium XIVa (P = 0.01), Clostridium XIVb (P = 0.04), Clostridium XVIII (P = 0.02), Collinsella (P = 0.005), Prevotella (P = 0.04), Prolixibacter (P = 0.02), Robinsoniella (P = 0.04), and Wandonia (P = 0.04) genera demonstrated statistically significant abundance among immature spermatozoa. CONCLUSIONS:Our results indicate that the human testicle harbours potential bacterial signature, though in a low-biomass, and could contribute to the seminal microbiome composition. Further, applying stringent decontamination methods is crucial for analysing microbiome in low-biomass site.