Nicotinamide mononucleotide production by non-recombinant Limosilactobacillus reuteri and nicotinamide adenine dinucleotide synthesizing lactic acid bacteria

UNLABELLED: β-nicotinamide mononucleotide (NMN) is a precursor of nicotinamide adenine dinucleotide (NAD⁺) and has the potential to suppress aging. Certain strains of lactic acid bacteria (LAB) can produce cofactors and vitamins through fermentation. Dozens of LAB species are considered to be safe for human ingestion, and some strains act as probiotics, which are live microorganisms that confer health benefits to the host. However, the production of NMN by LAB species, especially non-recombinant strains, has rarely been investigated. The purpose of this study was to identify LAB species that produce NMN and to develop a method to obtain a higher concentration of NMN using LAB. We quantified NMN concentrations in the supernatants of MRS broth cultures of 18 LAB type strains and determined that Limosilactobacillus reuteri JCM 1112T produced NMN. In this strain, the precursors of NMN were identified as NAD⁺, nicotinic acid, and nicotinamide based on the production of isotope-labeled NMN from these precursors labeled with stable isotopes. L. reuteri ME-989 produced NMN at 16.7 µmol/L by co-cultivation with Lactobacillus johnsonii JCM 2012T, which has a high NAD⁺-synthesizing ability. Non-recombinant L. reuteri and NAD⁺-synthesizing LAB may be useful for producing safe fermented products containing NMN. IMPORTANCE: β-nicotinamide mononucleotide (NMN) is a precursor of nicotinamide adenine dinucleotide (NAD⁺) and has the potential to suppress aging. Despite its increasing use in recent years, the production cost of NMN remains high. Certain strains of lactic acid bacteria (LAB), which are widely used in the fermentation of foods and are marketed as probiotics due to their safety and functional benefits, offer a promising alternative for the cost-effective production of functional compounds. However, the production of NMN by non-recombinant LAB has rarely been investigated except for some specific species. Our study has discovered that Limosilactobacillus reuteri produces NMN. The NMN production yield of this species was enhanced through co-cultivation with NAD⁺-synthesizing bacteria. These findings are significant for the development of safe, NMN-enriched fermented products.