We’re learning of more and more systems that have a microbiome – a community of bacteria, fungi and microbes living in harmony. Not just the gut but the mouth, the nose, the vagina… and would you believe, semen?

Yes, you read that right, semen has its own microbiome. And it’s crucial for male fertility.

According to US researchers from the Department of Urology at the ­University of California, the semen microbiome might play a key role in keeping sperm healthy and enhancing male fertility.

We know, in other situations, the microbiome is important for overall health. So the researchers investigated the semen microbiome to understand how it could affect infertility.

Exploring the effects of these ­naturally occurring microorganisms in semen could pave the way for ­developing new treatment to rectify deficiencies in sperm.

The study found that one bacterium in particular, Lactobacillus iners, may have a direct negative impact on male fertility. Men with more of this microbe tended to have issues with sperm motility – their movements – which is essential for fertilising an egg.

Previous research has revealed Lactobacillus iners can produce lactic acid, ­potentially leading to inflammation, capable of curbing sperm motility.

The study authors point out that existing research has already hinted at the link between L-iners and fertility, but most of the literature pertains to the vaginal microbiome and female factors. This is the first study to report a negative association between the bacterium and male fertility.

Researchers also discovered three types of bacteria in the Pseudomonas family were present in patients who had both normal and abnormal sperm numbers. Bacteria called Pseudomonas ­fluorescens and stutzeri were more common in men with abnormal sperm numbers, while ­Pseudomonas putida was less common in samples with abnormal sperm concentrations.

The findings indicate not every member of the same closely related group of bacteria will affect fertility in the same way, whether positively or ­negatively. In other words, even closely related bacteria may not always have the same correlation to fertility.

“There is much more to explore regarding the microbiome and its connection to male infertility,” said Vadim Osadchiy, lead author of the study at UCLA.

“However, these findings provide valuable insights that can lead us in the right direction for a deeper ­understanding of this correlation.

“Our research aligns with evidence from smaller studies and will pave the way for future, more comprehensive investigations to unravel the complex relationship between the semen microbiome and fertility.” Helpful work for shining a light on male infertility.