Characterization of the seminal bacterial microbiome of healthy, fertile stallions using next-generation sequencing

Abstract

High-throughput sequencing studies have shown the important role microbial communities play in the male reproductive tract, indicating differences in the semen microbial composition between fertile and infertile males. Most of these studies were made on human beings but little is known regarding domestic animals. Seminal bacteria studies made in stallions mostly focus on pathogenic bacteria and on their impact on reproductive technology. However, little is known about stallion commensal seminal microflora. That ultimately hinders our capacity to associate specific bacteria to conditions or seminal quality. Therefore, the aim of this study was to characterize the seminal microbial composition of 12 healthy, fertile stallion using next-generation sequencing. Hypervariable region V3 was chosen for bacterial identification. A total of nine phyla was detected. The most abundant ones were Bacteroidetes (46.50%), Firmicutes (29.92%) and Actinobacteria (13.58%). At family level, we found 69 bacterial families, but only nine are common in all samples. Porphyromonadaceae (33.18%), Peptoniphilaceae (14.09%), Corynebacteriaceae (11.32%) and Prevotellaceae (9.05%) were the most representative ones, while the Firmicutes phylum displayed the highest number of families (23, a third of the total). Samples showed high inter-subject variability. Findings previously described in other species notably differ from our findings. Families found in human such as Lactobacillaceae, Staphylococcaceae and Streptococcaceae only represented a 0.00%, 0.17% and 0.22% abundance in our samples, respectively. In conclusion, Porphyromonadaceae, Prevotellaceae, Peptoniphilaceae and Corynebacteriaceae families are highly represented in the seminal microbiome of healthy, fertile stallions. A high variation among individuals is also observed.

The Semen Microbiome and Semen Parameters in Healthy Stallions

“…Additionally, the positive effects of lactobacilli supplementation on sperm quality parameters have also been described in humans [ 19 , 20 ], mice [ 17 ], and broilers [ 18 ]. Stallion semen is not abundant in the Lactobacillus genus [ 10 , 11 ], but there are related bacterial families.…”

“…A dominant family in fertile stallions is Porphyromonadaceae [ 11 ]. According to our results, this family is highly abundant, as it represents almost the whole Bacteroidetes phylum.…”

“…Regarding this family, it is necessary to highlight that it is difficult to find in culture-based references, as it is a laborious process to culture bacteria. The other highly dominant family in stallion semen is Corynebacteriaceae [ 10 , 11 ], which has regularly been found in fertile individuals [ 10 , 23 , 37 , 38 , 39 , 40 ]. However, some authors consider it has an opportunistic character [ 22 , 33 , 41 ].…”

“…Regarding the strengths and limitations of our paper, next-generation sequencing is a better tool to characterize the seminal flora, as it overcomes laborious-to-culture bacteria [ 10 , 11 , 28 , 49 ]. However, the data process may be more complicated [ 50 ].…”

“…In recent years, the microbiome has proven to have a great impact on the systems they dwell on [ 5 , 6 , 7 , 8 , 9 ]. Unfortunately, the male reproductive tract has not received sufficient attention [ 10 , 11 ]. In the human species, however, some authors have already pointed out the influence of bacteria on semen quality [ 12 , 13 , 14 , 15 , 16 ].…”