A native phosphoribosyltransferase, PncB, is the key NMN synthase in Bacillus subtilis

Nicotinamide mononucleotide (NMN) is a precursor of NAD+, its efficient bio-production through microbial fermentation has rarely been reported. Bacillus subtilis was postulated to lack the inherent ability of NMN biosynthesis, however, certain level of NMN (53.67 mg/L) was detected in the fermentation broth containing nicotinamide. An endogenous enzyme (PncB) previously annotated as a nicotinic acid phosphotransferase was identified to be involved in the key synthetic reaction, since the deletion of pncB revoked the production of NMN, while the enhanced expression of PncB significantly increased the titer of NMN (110.0 mg/L). The structural simulation of PncB revealed the possible catalytic mechanisms of NMN forming. The NMN synthesis was further boosted by removing a possible deamidase (CinA), the yield of extracellular NMN reached 202.9 mg/L. After introducing the NMN transporter PnuC into the host cell, the fermentation level of NMN increased by another 65.34 %. And, with 20 g/L glucose and 10 g/L NAM supplemented in the medium, a maximal of 1.21 g/L of NMN was accumulated, signifying the potential of biological production of NMN using food-grade Bacillus subtilis.