Functional characterization of a novel β-glucosidase converting trillin to diosgenin from Enterococcus faecalis

Diosgenin, known as “medicinal gold”, is the main precursor for the synthesis of steroid hormone drugs. Currently, diosgenin is primarily produced industrially via the extraction of plant-derived steroidal saponins followed by acid hydrolysis, which generates substantial acidic wastewater. To address this environmental challenge, we sought to discover efficient glycosidases capable of converting steroidal saponins to diosgenin as a sustainable alternative to conventional acid hydrolysis. Through selective enrichment using dioscin as the sole carbon source, we isolated a strain Enterococcus faecalis D1 from rat gut microbiota. Subsequent genomic sequencing and functional annotation identified a potent steroid saponin β-glucosidase (designated EfD08) from E. faecalis D1, which represents the first reported bacterial β-glucosidase that efficiently converts trillin to diosgenin. EfD08 achieved soluble expression in Escherichia coli with an exceptionally high yield exceeding 200 mg/L, overcoming the low-expression bottleneck typical of reported steroid saponin glycosidases. Enzymatic characterization demonstrated that EfD08 exhibits robust activity with a half-life of approximately 100 h at its optimal temperature of 30 °C, which further extended to 355 h and 154 h in the presence of 5 mM Mg²⁺ or Mn²⁺, respectively. Furthermore, EfD08 displayed broad substrate specificity, efficiently hydrolyzing diverse steroid saponins (e.g., zingiberensis newsaponin, deltonin) and ginsenosides (e.g., Rb1, Rc). Given its high protein yield, catalytic efficiency, and stability, EfD08 emerges as a promising biocatalyst for the environmentally sustainable industrial production of diosgenin, other secondary saponins or sapogenins from natural saponins.