In a study recently published in iMetaMed, investigators from State Key Laboratory of Genome and Multi-omics Technologies at BGI-Research, BGI Precision Nutrition, Northwest A&F University, and Fudan University report that a single human-derived probiotic strain ameliorates the reproductive, metabolic, and behavioral features of polycystic ovary syndrome (PCOS) in a preclinical mouse model by restoring a disrupted communication pathway between the gut and the ovaries.
PCOS is the most common endocrine disorder among women of reproductive age, affecting an estimated 6% to 20% of this population worldwide. Beyond irregular ovulation and elevated androgens, the syndrome raises risks for type 2 diabetes and mood disorders, yet current treatments remain limited.
Growing evidence implicates the gut microbiota as a contributing factor in PCOS. However, precisely how an individual bacterial strain might correct this dysfunction has remained unclear. The study team addressed this gap by testing Bifidobacterium animalis subsp. lactis BGI-L99, a strain originally isolated from a healthy human gut and systematically selected from a curated library of cultivated human gut bacteria for its ability to modify bile acid metabolism. Re-analysis of a published human metagenomic dataset revealed that B. animalis, including BGI-L99, was significantly less abundant in women with PCOS than in healthy controls, suggesting the strain’s depletion may be associated with the disorder.
A strain-specific, mechanism-defined probiotic ameliorates PCOS in a preclinical model, advancing precision microbiome interventions toward future clinical strategies for women’s reproductive health.
In a mouse model of PCOS induced by the androgen precursor DHEA, daily oral administration of BGI-L99 for 21 days ameliorated multiple disease features. Treated mice regained regular estrous (reproductive) cycles, developed more corpora lutea (signs of improved ovulatory function), and showed fewer ovarian cysts. Serum testosterone fell while estradiol rose, and fasting glucose and blood lipid levels improved. BGI-L99 also alleviated depression-like and anxiety-like behaviors.
BGI-L99 restores bile acids that activate TGR5-IL-22 immune signaling, establishing a traceable gut-to-ovary relay that links a defined probiotic to reproductive improvement in PCOS mice.
The study traced these improvements to a molecular relay originating in the gut. BGI-L99 reshaped the gut microbial community, reducing potentially harmful species such as Phocaeicola vulgatus while promoting beneficial bacteria. This microbial shift restored depleted levels of two key bile acids, chenodeoxycholic acid (CDCA) and tauroursodeoxycholic acid (TUDCA), both now recognized as signaling molecules that carry messages between the gut and distant organs. The restored bile acids activated the TGR5 receptor on intestinal immune cells, boosting production of interleukin-22 (IL-22), a protective immune protein that helps maintain tissue integrity. Elevated IL-22 was detected in both serum and ovarian tissue, suggesting that this gut-derived immune signal may contribute to the observed reproductive improvements.
BGI-L99 is less abundant in a human PCOS cohort; in a mouse model, oral supplementation restored ovarian structure and normalized sex hormones, linking the strain’s depletion to amelioration of key PCOS phenotypes.
To test whether bile acids were the operative link, the researchers conducted a separate experiment in which PCOS mice received oral CDCA or TUDCA alone. Both bile acids independently recapitulated several key effects of BGI-L99, including improved reproductive cycling, reduced cystic follicles, normalized sex hormones, and elevated IL-22. This causal evidence strengthens the case that the gut microbiota, bile acid, and IL-22 pathway is the primary route through which BGI-L99 exerts its effects in the mouse model.
Direct bile acid supplementation independently recapitulated the probiotic’s ovarian and immune effects in the mouse model, providing causal evidence that bile acid restoration is a key mechanistic link between gut microbiota and PCOS amelioration.
Computational modeling further revealed that BGI-L99 acts as a nutritional hub in the gut ecosystem; in silico removal of the strain caused a 36.7% loss in community metabolic output, underscoring the strain’s role in sustaining microbial balance. Together with the strain’s human origin and defined mechanism of action, linking a specific bacterium through bile acid metabolites and an immune signal to reproductive and metabolic outcomes, these findings position BGI-L99 within the emerging field of strain-specific, mechanism-defined microbiome interventions.
Extending this preclinical work to well-designed human clinical trials will be essential to evaluate whether BGI-L99 can support similar improvements in women with PCOS. If confirmed in clinical settings, such strain-specific approaches could eventually broaden the options available to women managing this common condition.
All animal procedures were approved by the relevant institutional animal ethics committee and conducted in accordance with institutional guidelines for the care and use of laboratory animals.