Abstract
As one of the most significant steroid hormone precursors, androst-1,4-diene-3,17-dione (ADD) could be used to synthesize many valuable hormone drugs. The microbial transformation of sterols to ADD has received extensive attention in recent years. In a previous study, Mycobacterium neoaurum JC-12 was isolated and converted sterols to the major product, ADD. In this work, we enhanced ADD yield by improving the cell intracellular environment. First, we introduced a nicotinamide adenine dinucleotide (NADH) oxidase from Bacillus subtilis to balance the intracellular NAD+ availability in order to strengthen the ADD yield. Then, the catalase gene from M. neoaurum was also over-expressed to simultaneously scavenge the generated H2O2 and eliminate its toxic effects on cell growth and sterol transformation. Finally, using a 5 L fermentor, the recombinant strain JC-12yodC-katA produced 9.66 g/L ADD, which increased by 80% when compared with the parent strain. This work shows a promising way to increase the sterol transformation efficiency by regulating the intracellular environment.
Highlights
As one of the well-known androgen steroids, androst-1,4-diene-3,17-dione (ADD) was extensively used as an important precursor for the synthesis of steroid hormone medicines in the pharmaceutical industry [1]
These results indicate that the intracellular redox balance in JC-12yodC was not disturbed, which could explain why its cell growth was not obviously affected
The catalase expression is needed for achieving high sterol conversion efficiency. These results indicate that the regulation of the intracellular NAD+ /NADH and H2 O2 level possibly due to the lack of catalase and peroxidase activity for this strain, causing an inability to eliminate H2O2 in a timely fashion and allowing for an easy accumulation to a high concentration
Summary
As one of the well-known androgen steroids, androst-1,4-diene-3,17-dione (ADD) was extensively used as an important precursor for the synthesis of steroid hormone medicines in the pharmaceutical industry [1]. ADD was obtained from natural steroids such as sapogenin and diosgenin using multistep chemical degradation and modification methods. The well-established route of sapogenin and diosgenin to ADD has many drawbacks, such as waste of land resources, high-cost processes, relatively low yields, and high pollution [2]. With the awareness of environmental protection, biological technology has become the development tendency and inevitable choice for the steroid medical industry [3,4]. Since the discovery of microbial sterols side-chain degradation to 17-ketosteroids, sterol biotransformation has become a promising alternative way to synthesize valuable steroid intermediates in the pharmaceutical industry [5].
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