Multigram-scale stereoselective synthesis of neurosteroid isomers by gut microbial isolates using plant biomass-derived medium

Neurosteroids are vital therapeutics for mood disorders, with FDA-approved allopregnanolone (Zulresso) for postpartum depression and zuranolone for major depressive disorder representing breakthrough treatments. However, current production methods rely on costly animal-derived sources or non-stereoselective chemical synthesis that require extensive chiral purification steps. Here, we present a sustainable microbial platform utilizing gut bacteria and a completely plant-based medium for stereoselective neurosteroid biosynthesis. Through bioinformatics- and structural biology-guided screening of more than 3000 bacterial isolates, we identified three anaerobic gut strains exhibiting distinct stereospecificities: Holdemania filiformis produces isopregnanolone (3β-hydroxy-5α-pregnan-20-one), Clostridium innocuum generates epipregnanolone (3β-hydroxy-5β-pregnan-20-one), and Hungatella effluvii synthesizes pregnanolone (3α-hydroxy-5β-pregnan-20-one). We developed Molasses-Okara Medium (MOM), a fully plant-derived composite medium combining sugarcane molasses with enzymatically hydrolyzed okara devoid of animal-derived components. In multigram batch whole-cell biotransformation trials using MOM, we achieved >95% progesterone conversion into target neurosteroid isomers. The inherent stereoselectivity of these whole-cell biotransformations bypasses downstream chiral chromatographic separation, enabling pharmaceutical-grade product recovery through a simple open-column purification. Compared to using peptone-yeast-glucose media for whole-cell biotransformation, MOM reduced production costs by 90% and carbon footprint by 95% that embodies sustainable bioeconomy principles in pharmaceutical biotechnology.