Microbial steroid biotransformation: Regio- and stereo selective 17β-reduction by Priestia aryabhattai.

The conversion of 17-oxosteroids to 17β-hydroxysteroids stands as a pivotal process in the synthesis of numerous steroidal drugs and intermediates. This study explored the potential of the strain Priestia aryabhattai (IICT-BC-1279) to catalyze the reduction of the C-17 carbonyl group in androst-4-ene-3,17-dione (AD), resulting in the exclusive production of testosterone (TS) through its 17β-hydroxysteroid dehydrogenase (17β-HSD) activity. Optimal conditions for this reduction were achieved at pH 7.0 and 25 °C, with supplementation of AD as an inducer (0.01 g/L), 1 % Tween 80 (w/v) and ethanol as co-solvent. Under these optimized parameters, 0.5 g/L AD was efficiently converted to TS as a sole product, achieving a yield of > 95 % and diastereomeric excess (d.e) of > 99 % within 48 h. The absence of by-products in this microbial 17β-reduction process simplifies product purification, highlighting the strain's potential as a valuable biocatalyst for this essential transformation. Additionally, the conversion of androsta-1,4-diene-3,17-dione (ADD) to (+)-Boldenone (BD) was studied to explore substrate scope.