The impact of vasectomy on the seminal microbiome: possible implications and source of microbes.

study questionDoes vasectomy alter the seminal microbiome, and what proportions of seminal microorganisms originate from the urinary and upper reproductive tract? SUMMARY ANSWER: Vasectomy is associated with modest shifts in the seminal microbial community structure, where inter-individual variability prevails, and the semen shares over 60% of bacterial communities with urine, suggesting an influence of the urinary tract and upstream genitourinary compartments on the seminal microenvironment. WHAT IS KNOWN ALREADY: The semen harbours a polymicrobial community whose origin is not fully understood. Also, the effect of vasectomy, a common sterilization procedure, on seminal microenvironment is not clear. Recent studies with a limited sample size suggest that part of the seminal microbiome may derive from the upper genital tract, and that vasectomy may alter seminal microbial composition, potentially revealing testicular or epididymal microbial contributions. STUDY DESIGN SIZE DURATION: This prospective cohort study including 82 men undergoing vasectomy, with paired semen and urine samples collected before and 3 months after the procedure. PARTICIPANTS/MATERIALS SETTING

methodsPaired semen and urine samples were collected pre- and post-vasectomy. The seminal and urine microbiome was analysed by sequencing the V4 hypervariable region of the 16S rRNA gene. Amplicon sequence variants were decontaminated using rigorous negative-control-based methods. Microbial diversity, taxonomic composition, and differential abundance were assessed, and functional profiles were predicted using PICRUSt2. MAIN RESULTS AND THE ROLE OF CHANCE: More than 60% of seminal bacterial genera were also present in urine, indicating substantial overlap. Vasectomy significantly altered β-diversity; however, the effect was small, and several predicted functional pathways were detected, including lipid metabolism. Although some genera differed between pre- and post-vasectomy samples, these did not remain significant after false discovery rate (FDR) correction. These findings should be interpreted considering the prevailing inter-individual variability and shared urinary-seminal taxa. LARGE SCALE DATA: The 16S rRNA gene sequencing data have been uploaded to the SRA database under BioProject ID PRJNA1355064. LIMITATIONS REASONS FOR CAUTION: The main limitations of the study are the use of 16S rRNA gene sequencing, which limits species-level resolution, the lack of repetitive sampling, and the absence of absolute bacterial load quantification. Also, the functional pathway analyses present predictive estimates from the sequencing data rather than from direct measurements of the microbial metabolic activity. WIDER IMPLICATIONS OF THE

findingsVasectomy may induce subtle changes in the seminal microenvironment by modifying microbial composition and metabolic functions, as indicated by these exploratory analyses. Nevertheless, our study findings should not be interpreted as evidence against vasectomy, rather as novel information to better understand the dynamics of the seminal microbiome. Whether the microbial changes have any effect on the male urogenital health requires further research. STUDY FUNDING/COMPETING INTERESTS: This work was supported by projects ENDORE (SAF2017-87526-R); Endo-Map (PID2021-12728OB-I00), and ROSY (CNS2022-135999), funded by MICIU/AEI/10.13039/501100011033 and by FEDER, EU; I.L.-B. and C.M.T. are supported by the FPU22/03045 grant and FPU23/01576, awarded by MCIN/AEI/10.13039/501100011033, respectively; additionally, S.A. obtained a mobility grant for senior researchers to do a research stay abroad funded by the Spanish Ministry of Science, Innovation and Universities (ref. PRX24/00372); I.P.-P. and A.S.-L. were supported by Becas Fundación Ramón Areces para Estudios Postdoctorales-Convocatorias XXXVI-XXXV para Ampliación de Estudios en el Extranjero en Ciencias de la Vida y de la Materia; A.S.-L. is supported by the Estonian Research Council (grant no. PSG1082); funding for open access charge: Universidad de Granada / CBUA. The authors declare no competing interests.