Regulation of NAD (H) Pool by Overexpression of Nicotinic Acid Phosphoribosyltransferase for AD (D) Production in Mycobacterium neoaurum

Phytosterol (PS) biotransformation to androst-4-ene-3,17-dione (AD) and androst-1,4-diene-3,17-dione (ADD) was proposed a NAD+-dependence process in Mycobacterium neoaurum (MNR). To improve the PS biotransformation, overexpression of nicotinic acid phosphoribosyltransferase (NAPRTase), a rate limiting enzyme of NAD (H) synthesis encoded by the pncB gene, resulted in a significant increase in AD (D) production, the peak molar yield of AD (D) (94.9%) was achieved. Furthermore, the cell growth and glucose consumption were improved due to the overexpression of NAPRTase. Analysis of intracellular cofactor levels showed significant increases in NAD (H) pool size (13.8%), and the NAD+/NADH ratio (22.2%). The present study indicates that the AD (D) production could be improved by increasing the intracellular NAD+ level and NAD+/NADH ratio in MNR. It is provided further evidence that regulation of NAD (H) pool and NAD+/NADH ratio was important for producing the NAD+-dependent microbial metabolite.