Abstract
The steroid metabolites 9-hydroxy-androstenedione (9-OH-AD), androstadienedione (ADD) and androstenedione (AD) are important steroidal pharmaceuticals. In order to raise the production of steroid metabolites, an efficient resting cell phytosterol bioconversion process was developed to produce 9-OH-AD in the presence of hydroxypropyl-b-cyclodextrin (HP-b-CD). Cell growth medium containing phytosterol as an inducer positively improved cell activity. Under aerobic conditions, bioconversion proceeded at 70 g L –1 phytosterol in the presence of HP-b-CD (the optimized molar ratio of HP-b-CD/phytosterol was 1:1) with 30 g L –1 resting Mycobacterium neoaurum NwIB-yV cells (cell dry mass) in a 5-L bioreactor, where 9-OH-AD production and space-time yield reached 36.4 g L –1 and 9.1 g L –1 d –1 , respectively. The recycling of cells and HP-b-CD enables cost-saving and industrial applications. This bioprocess was also applied for the production of ADD and AD. The production of these steroid metabolites was much higher than that reported in previous studies.
Highlights
Microbial sterol bioconversion is a powerful approach for the production of key steroidal intermediates, such as 9-hydroxy-androstenedione (9-OH-AD), androstadienedione (ADD) and androstenedione (AD)
We studied the effects of substrate solubilization with HP-b-CD and the use of resting cell bioconversion on the conversion of a high concentration of phytosterol to 9-OH-AD
Due to the hydrophobic characteristic of phytosterol, the solubility is low in aqueous solutions, which results in a poor availability of the substrate
Summary
Microbial sterol bioconversion is a powerful approach for the production of key steroidal intermediates, such as 9-hydroxy-androstenedione (9-OH-AD), androstadienedione (ADD) and androstenedione (AD). These steroid metabolites are valuable starting materials for the preparation of steroidal pharmaceuticals which are widely used as anti-tumor, anti-inflammatory, anti-microbial, anti-viral, and anti-fungal drugs, etc.[1] AD and ADD are required for the commercial production of corticosteroids, mineralocorticoids, oral contraceptives, and other pharmaceutical steroids. Many approaches have been taken to improve the solubility and bioavailability of sterols to the bacteria and increase the efficiency of microbial sterol bioconversion, including the use of the cyclodextrin (CD) complexation technique[5] and CDs have a doughnut-shaped molecular structure, with a hydrophilic outer surface and a hydrophobic cavity.[8] CDs and their derivatives can form host-guest complexes with hydrophobic compounds in their internal cavities. Hydroxypropyl-b-cyclodextrin (HP-b-CD), a CD derivative, has a greater capacity for complex formation than CD, and it has been recently used for the bioconversion of phytosterol to ADD and AD.[5,10]
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