LAUSR

HIGHLIGHTSProgesterone converted by the fungus Aspergillus sojae PTCC 5196 produced testololactone.The production of testololactone indicated fungal Baeyer‐Villiger monooxygenase (BVMO) activity.Substrate‐induced cultures have a decisive impact on the metabolism of progesterone.Progesterone, a C‐21 steroidal compound, induced 17&bgr;‐acetyl side chain cleavage.Androstenedione, testosterone, and DHEA, C‐19 steroidal substances, induced ring‐D oxidation. ABSTRACT Microbial transformations are capable of producing steroid substances difficult to synthesize by chemical methods. Strains belonging to the genus Aspergillus are effective facilitators of microbial biotransformations due to their enzymatic diversity. In this study, the biotransformation of progesterone by the fungus Aspergillus sojae (A. sojae) PTCC 5196 was examined. Analysis of the bioconversion process revealed that progesterone was converted to testololactone through a three‐step pathway (17&bgr;‐acetyl side chain cleavage, 17&bgr;‐hydroxyl oxidation, and oxygenative lactonization of 17‐ketone), indicating the presence of Baeyer‐Villiger monooxygenase (BVMO) activity in the fungal strain. GC analysis confirmed the production of testololactone with a yield of 99% in 24h. Faster testololactone production was induced in the presence of both C‐21 (progesterone) and C‐19 (androstenedione, testosterone, and dehydroepiandrosterone [DHEA]) steroid substances. Due to the high biotransformation rate observed in the present study, A. sojae may be a novel and promising candidate in the production of testololactone.