Systematic Engineering of Escherichia coli for Efficient Production of Nicotinamide Mononucleotide From Nicotinamide

Establishing a novel pathway for the biosynthesis of nicotinamide mononucleotide

Nicotinamide mononucleotide (NMN) is a pivotal molecule within the realm of metabolic health, serving as a precursor to nicotinamide adenine dinucleotide (NAD+), a critical coenzyme in cellular energy metabolism. In recent years, the biological production of NMN has garnered significant interest. In this study, we developed the novel NRK-dependent synthesis routes for NMN production. Two strategies were designed to supply D-ribose-1-phosphate (R-1-P): (1) phosphorylation of exogenous D-ribose to ribose-5-phosphate (R-5-P) using engineered ribokinase (RK), followed by isomerization to R-1-P; (2) R-5-P synthesis from glucose through the pentose phosphate pathway. An optimized in vitro multi-enzyme cascade (XapA/PNP/NRK, PPM, NRK) identified NRK as the most efficient catalyst for NMN biosynthesis from D-ribose and niacinamide. In Escherichia coli, overexpression of this cascade, knockout of competing pathways, and secretion enhancement via a pelB signal peptide-fused PnuC transporter achieved an NMN titer of 62.0 mg L-¹ .This work provides a viable alternative for the biosynthesis of NMN.

Enhancing nicotinamide mononucleotide production in Escherichia coli through systematic metabolic engineering

Nicotinamide mononucleotide (NMN) serves as a crucial precursor in the biosynthesis of NAD+ and has garnered significant attention in the food, dietary supplement, and cosmetic industries. This study engineered an Escherichia coli strain for enhancing NMN production. Firstly, the strain with reduced NMN degradation and the ability to transport NMN extracellularly was constructed. Meanwhile, the gene encoding nicotinamide phosphoribosyltransferase (pncA) was disrupted to minimize substrate nicotinamide (NAM) degradation. Then, the induction starting point was optimized to alleviate the metabolic burden on the engineered strain. Subsequently, systematic remodeling of E. coli's glucose metabolism was conducted to enhance its suitability for NMN production by overexpressing key enzymes of the pentose phosphate pathway (Zwf and Gnd), knocking out genes related to the Entner-Doudoroff pathway (gntR and edd), and further attenuating the glycolytic pathway. Then, we concentrated on optimizing the cellular metabolic state, meticulously balancing intracellular redox homeostasis. Finally, using glucose and 2 g/L of NAM as substrates, the extracellular NMN yield reached 4.96 g/L, which is the highest yield reported so far in similar research. These findings contribute to the commercial production of NMN and offer valuable insights for constructing efficient cell factories for other nucleotide compounds.

Metabolic reprogramming and machine learning-guided cofactor engineering to boost nicotinamide mononucleotide production in Escherichia coli

Nicotinamide mononucleotide (NMN) is a bioactive compound in NAD(P)+ metabolism, which exhibits diverse pharmaceutical interests. However, enhancing NMN biosynthesis faces the challange of competing with cell growth and disturbing intracellular redox homeostasis. Herein, we boosted NMN production in Escherichia coli by reprogramming central carbon metabolism with a machine learning (ML)-guided cofactor engineering strategy. Engnieering NMN biosynthesis-related pathway directed carbon flux toward NMN with the NADPH level increased by 73 %, which, although enhanced NMN titer (2.45 g/L), impaired cell growth. A quorum sensing (QS)-controlled cofactor engineering system was thus contructed and optimized by ML models to address redox imbalance, which led to 3.04 g/L NMN with improved cell growth. The final strain S344 produced 20.13 g/L NMN in fed-batch fermentation. This study showed that perturbation on cofactor level is a crucial limiting factor for NMN biosynthesis, and proposed a novel ML-guided strategy to manipulate intracellular redox state for efficient NMN production.

Microbial Production of Nicotinamide Mononucleotide: Key Enzymes Discovery, Host Cells Selection, and Pathways Design and Optimization

As an important bioactive substance in cells, nicotinamide mononucleotide (NMN) has been proven to play an important role in antiaging, treatment of neurodegenerative diseases, and cardioprotection. It presents a high potential for application in the research fields of functional foods, cosmetics, healthcare products, and active pharmaceuticals. With the increased demand, whether NMN can achieve large-scale industrial production has been a wide concern. The chemical synthesis method of NMN mainly faces the problems of separation, purification, and complex process control; in contrast, biosynthesis methods such as microbial fermentation and enzyme catalysis are considered to be the mainstream of the future industrial production of NMN due to the advantages of environmental friendliness, high efficiency, and simple separation. This review first describes the physiological functions of NMN and the related areas of its applications. Subsequently, it focuses on the research progress on different synthetic pathways of NMN in biosynthetic approaches, mining and modification of key enzymes, chassis cell design and optimization, and whole-cell catalysis. Meanwhile, the regulatory strategies, methods, and process control of the microbial synthesis of NMN are also elaborated, and the synthesis efficiencies of different chassis cells are systematically compared. Finally, this review summarizes the existing problems and challenges of microbial synthesis of NMN and proposes future strategies and directions to address these issues. This work provides technical references and a theoretical basis for researching efficient NMN microbial synthesis and application.

Improving Biosynthesis Efficiency of Nicotinamide Mononucleotide by ATP Recycling Engineering and Condition Optimization

Nicotinamide mononucleotide (NMN) is a very important bioactive nucleotide that is of great help to human health. However, its widespread application has been limited by its high production costs, especially the cost of the core substrates, coenzyme, and enzymes. In this study, the ADP/GDP-polyphosphate phosphotransferase RhPPK2 originating from Rhodobacter sphaeroides was successfully expressed in Escherichia coli with high-level solubility, and the enzyme activity in the lysate supernatant reached 21.9 ± 0.65 U/mL. And then, the temperature profiles, pH profiles, and kinetic parameters of purified reRhPPK2 were systematically characterized, which demonstrate its potential for application in enzymatic ATP regeneration systems. Furthermore, the introduction of reRhPPK2 for ATP regeneration significantly enhanced NMN production efficiency, achieving a 2.3-fold increase compared to the conventional ATP supplementation method. Finally, the production efficiency of NMN was further improved by a single-factor experiment and L9(34) orthogonal design, and the yield was up to 14.6 ± 0.51 g/L, about 5.4 times of the initial yield. This research substantially reduced NMN production costs and established a robust foundation for industrial-scale NMN production.

Intelligent biomanufacturing of water-soluble vitamins

Given the crucial role of water-soluble vitamins in the human body and the rising demand for natural sources, their biosynthesis has gained the attention of researchers. This review offers a comprehensive look at recent progress in water-soluble vitamin biosynthesis, emphasizing synthetic biotechnology for green biomanufacturing. Specifically, it encompasses the optimization of biological components, pathways, and systems, as well as energy metabolism regulation, stress-tolerance enhancement, high-throughput screening, and the upscaling of production processes. It also envisages intelligent biomanufacturing platforms, highlighting the role of systems biology and artificial intelligence (AI), and proposes future research directions, such as integrating AI-driven metabolic models, enzyme engineering, and cell-free systems, to address limitations in the efficiency, toxicity, and scalability of water-soluble vitamin production.

Cell-free biocatalysis for co-production of nicotinamide mononucleotide and ethanol from Saccharomyces cerevisiae and recombinant Escherichia coli

Cell-free enzyme systems have emerged as a promising approach for producing various biometabolites, offering several advantages over traditional whole-cell systems. This study presents an approach to producing nicotinamide mononucleotide (NMN) by combining a Saccharomyces cerevisiae cell-free enzyme with a recombinant Escherichia coli cell-free enzyme. The system leverages the ATP generated by yeast during ethanol fermentation to produce NMN in the presence of nicotinamide (NAM) as a substrate. The optimal cell-free enzyme concentration and substrate concentration were investigated to maximize NMN production. The results showed that combined cell-free enzymes led to increased NMN and ethanol yields, with a maximum production of 1.5 mM NMN (2.7-fold) and ethanol production of 0.45 g/L achieved (1.6-fold) compared to individual cell-free enzymes. Furthermore, the study demonstrated that the protein concentration affected NMN production, with optimal production achieved at 5 g/L. This study demonstrates the potential of integrating multiple metabolic pathways in a single cell-free system, paving the way for the development of more efficient and sustainable bioproduction processes.

High-Level Production of Nicotinamide Mononucleotide by Engineered Escherichia Coli

Nicotinamide mononucleotide (NMN), a key precursor of NAD+, is a promising nutraceutical due to its excellent efficacy in alleviating aging and disease. The bioproduction of NMN faces challenges related to incomplete metabolic engineering and insufficient metabolic flux. Here, we constructed an NMN synthesis pathway in Escherichia coli BW25113 by deleting the competitive pathway genes and introducing three heterologous genes encoding the key enzymes nicotinamide phosphoribosyltransferase (NAMPT), phosphoribosyl pyrophosphate synthetase and an NMN transporter. Next, the identification of a highly active NAMPT and optimization of gene expression markedly increased the conversion of NAM to NMN, with a titer of 3503.85 mg/L in shake flasks. Furthermore, by facilitating the coutilization of glucose and xylose, more metabolic flux was diverted toward PRPP biosynthesis, resulting in an NMN titer of 15.66 g/L through whole-cell catalysis and 46.66 g/L in a 2-L bioreactor. This represents the highest NMN yield reported to date, exhibiting great potential for initiating sustainable industrial production of NMN.

Gastrointestinal jumbo phages possess independent synthesis and utilization systems of NAD. MICROBIOME 2024;12:268. [PMID: 39707494 DOI: 10.1186/s40168-024-01984-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

BACKGROUND

Jumbo phages, phages with genomes > 200 kbp, contain some unique genes for successful reproduction in their bacterial hosts. Due to complex and massive genomes analogous to those of small-celled bacteria, how jumbo phages complete their life cycle remains largely undefined.

RESULTS

In this study, we assembled 668 high-quality jumbo phage genomes from over 15 terabytes (TB) of intestinal metagenomic data from 955 samples of 5 animal species (cow, sheep, pig, horse, and deer). Within them, we obtained a complete genome of 716 kbp in length, which is the largest phage genome so far reported in the gut environments. Interestingly, 174 out of the 668 jumbo phages were found to encode all genes required for the synthesis of NAD+ by the salvage pathway or Preiss-Handler pathway, referred to as NAD-jumbo phage. Besides synthesis genes of NAD+, these NAD-jumbo phages also encode at least 15 types of NAD+-consuming enzyme genes involved in DNA replication, DNA repair, and counterdefense, suggesting that these phages not only have the capacity to synthesize NAD+ but also redirect NAD+ metabolism towards phage propagation need in hosts. Phylogenetic analysis and environmental survey indicated NAD-jumbo phages are widely present in the Earth's ecosystems, including the human gut, lakes, salt ponds, mine tailings, and seawater.

CONCLUSION

In summary, this study expands our understanding of the diversity and survival strategies of phages, and an in-depth study of the NAD-jumbo phages is crucial for understanding their role in ecological regulation. Video Abstract.

Biological production of nicotinamide mononucleotide: a review

Nicotinamide mononucleotide (NMN) presents significant therapeutic potential against aging-related conditions, such as Alzheimer's disease, due to its consistent and strong pharmacological effects. Aside from its anti-aging effect, NMN is also an emerging noncanonical cofactor for orthogonal metabolic pathways in the field of biomanufacturing. This has significant advantages in the field of metabolic engineering, allowing cells to produce unnatural chemicals without disrupting the natural cellular processes. NMN is produced through both the chemical and biological methods, with the latter being more environmentally sustainable. The primary biological production pathway centers on the enzyme nicotinamide phosphoribosyltransferase, which transforms nicotinamide and phosphoribosyl pyrophosphate to NMN. Efforts to increase NMN production have been explored in microorganisms, such as: Escherichia coli, Bacillus subtilis, and yeast, serving as biocatalysts, by rewiring their metabolic processes. Although most researchers are focusing on genetically and metabolically manipulating microorganisms to act as biocatalysts, a growing number of studies on cell-free synthesis are emerging as a promising strategy for producing NMN. This review explores the different biological production techniques of NMN employing microorganisms. This article, in particular, is essential to those who are working on NMN production using microbial strain engineering and cell-free systems.

Harnessing lactic acid bacteria for nicotinamide mononucleotide biosynthesis: a review of strategies and future directions

Nicotinamide mononucleotide (NMN), one of the crucial precursors of nicotinamide adenine dinucleotide, has garnered considerable interest for its pharmacological and anti-aging effects, conferring potential health and economic benefits for humans. Lactic acid bacteria (LAB) are one of the most important probiotics, which is commonly used in the dairy industry. Due to its probiotic properties, it presents an attractive platform for food-grade NMN production. LAB have also been extensively utilized to enhance the functional properties of pharmaceuticals and cosmetics, making them promising candidates for large-scale up synthesis of NMN. This review provides an in-depth analysis of various metabolic engineering strategies, including enzyme optimization, pathway rewiring, and fermentation process enhancements, to increase NMN yields in LAB. It explores both CRISPR/Cas9 and traditional methods to manipulate key biosynthetic pathways. In particular, this study discussed future research directions, emphasizing the application of synthetic biology, systems biology, and AI-driven optimization to further enhance NMN production. It provides invaluable insights into developing scalable and industrially relevant processes for NMN production to meet the growing market demand.

An overview of engineering microbial production of nicotinamide mononucleotide

As the human body gradually ages, the cellular level of NAD+ will decline, which has been found to be related to a variety of age-related diseases. As a precursor of NAD+, NMN is able to effectively promote the synthesis of NAD+ with no significant side effects. Microbial production of NMN holds the potential to lower the production cost and facilitate its wide application. In this review, based on the metabolic pathway of NAD+, we summarize recent advances of metabolic engineering strategies for NMN biosynthesis. An outlook for future optimization to improve NMN production is also discussed.

De novo biosynthesis and nicotinamide biotransformation of nicotinamide mononucleotide by engineered yeast cells

β-Nicotinamide mononucleotide (NMN) is a precursor of NAD+ in mammals. Research on NAD+ has demonstrated its crucial role against aging and disease. Here two technical paths were established for the efficient synthesis of NMN in the yeast Pichia pastoris, enabling the production of NMN from the low-cost nicotinamide (NAM) or basic carbon sources. The yeast host was systematically modified to adapt to the biosynthesis and accumulation of NMN. To improve the semi-biosynthesis of NMN from NAM, nicotinamide phosphoribosyltransferases were expressed intracellular to evaluate their catalytic activities. The accumulation of extracellular NMN was further increased by the co-expression of an NMN transporter. Fine-tuning of gene expression level produced 72.1 mg/L NMN from NAM in flasks. To achieve de novo biosynthesis NMN, a heterologous biosynthetic pathway was reassembled in yeast cells. Fine-tuning of pathway nodes by the modification of gene expression level and enhancement of precursor generation allowed efficient NMN synthesis from glucose (36.9 mg/L) or ethanol (57.8 mg/L) in flask. Lastly, cultivations in a bioreactor in fed-batch mode achieved an NMN titre of 1004.6 mg/L at 165 h from 2 g NAM and 868 g glucose and 980.4 mg/L at 91 h from 160 g glucose and 557 g ethanol respectively. This study provides a foundation for future optimization of NMN biosynthesis by engineered yeast cell factories.

High-efficient preparation of β-nicotinamide mononucleotides by crude enzymes cascade catalytic reaction

β-nicotinamide mononucleotide (β-NMN) is a key precursor of nicotinamide adenine dinucleotide, and becomes attractive in the nutrition and health care fields, but its enzymatic synthesis is expensive. In this study, a six-enzyme cascade catalytic system was constructed to produce β-NMN. Using D-ribose and nicotinamide as substrates, the β-NMN yield reached 97.5 % catalyzed by purified enzymes. Then, after knocking out the genes encoding proteins that consume β-NMN in E. coli BL21(DE3), the similar β-NMN yield, 97.2 %, using the crude enzymes could be also obtained. After that, β-NMN synthesis was performed under increased substrate concentration, and 'modular' crude enzymes cascade catalytic reaction system was proposed to reduce the inhibition of polyphosphate on ribose-phosphate diphosphokinase activity, and the β-NMN yield reached 78.4 % at 10 mM D-ribose, which is 1.82 times of that in 'one-pot' reaction and represents the highest β-NMN preparation level with phosphoribosylpyrophosphate as the core reported till now.

Exploring the De Novo NMN Biosynthesis as an Alternative Pathway to Enhance NMN Production

Nicotinamide mononucleotide (NMN) serves as a precursor for NAD+ synthesis and has been shown to have positive effects on the human body. Previous research has predominantly focused on the nicotinamide phosphoribosyltransferase-mediated route (NadV-mediated route) for NMN biosynthesis. In this study, we have explored the de novo NMN biosynthesis route as an alternative pathway to enhance NMN production. Initially, we systematically engineered Escherichia coli to enhance its capacity for NMN synthesis and accumulation, resulting in a remarkable over 100-fold increase in NMN yield. Subsequently, we progressively enhanced the de novo NMN biosynthesis route to further augment NMN production. We screened and identified the crucial role of MazG in catalyzing the enzymatic cleavage of NAD+ to NMN. And the de novo NMN biosynthesis route was optimized and integrated with the NadV-mediated NMN biosynthetic pathways, leading to an intracellular concentration of 844.10 ± 17.40 μM NMN. Furthermore, the introduction of two transporters enhanced the uptake of NAM and the excretion of NMN, resulting in NMN production of 1293.73 ± 61.38 μM. Finally, by engineering an E. coli strain with optimized PRPP synthetase, we achieved the highest NMN production, reaching 3067.98 ± 27.25 μM after 24 h of fermentation at the shake flask level. In addition to constructing an efficient E. coli cell factory for NMN production, our findings provide new insights into understanding the NAD+ salvage pathway and its role in energy metabolism within E. coli.

Advances in the Synthesis and Physiological Metabolic Regulation of Nicotinamide Mononucleotide

Nicotinamide mononucleotide (NMN), the direct precursor of nicotinamide adenine dinucleotide (NAD+), is involved in the regulation of many physiological and metabolic reactions in the body. NMN can indirectly affect cellular metabolic pathways, DNA repair, and senescence, while also being essential for maintaining tissues and dynamic metabolic equilibria, promoting healthy aging. Therefore, NMN has found many applications in the food, pharmaceutical, and cosmetics industries. At present, NMN synthesis strategies mainly include chemical synthesis and biosynthesis. Despite its potential benefits, the commercial production of NMN by organic chemistry approaches faces environmental and safety problems. With the rapid development of synthetic biology, it has become possible to construct microbial cell factories to produce NMN in a cost-effective way. In this review, we summarize the chemical and biosynthetic strategies of NMN, offering an overview of the recent research progress on host selection, chassis cell optimization, mining of key enzymes, metabolic engineering, and adaptive fermentation strategies. In addition, we also review the advances in the role of NMN in aging, metabolic diseases, and neural function. This review provides comprehensive technical guidance for the efficient biosynthesis of NMN as well as a theoretical basis for its application in the fields of food, medicine, and cosmetics.

Biosynthesis of β-nicotinamide mononucleotide from glucose via a new pathway in Bacillus subtilis

Introduction

β-nicotinamide mononucleotide (β-NMN) is an essential precursor of nicotinamide adenine dinucleotide (NAD+) and plays a key role in supplying NAD+ and maintaining its levels. Existing methods for NMN production have some limitations, including low substrate availability, complex synthetic routes, and low synthetic efficiency, which result in low titers and high costs.

Methods

We constructed high-titer, genetically engineered strains that produce NMN through a new pathway. Bacillus subtilis WB600 was used as a safe chassis strain. Multiple strains overexpressing NadE, PncB, and PnuC in various combinations were constructed, and NMN titers of different strains were compared via shake-flask culture.

Results

The results revealed that the strain B. subtilis PncB1-PnuC exhibited the highest total and extracellular NMN titers. Subsequently, the engineered strains were cultured in a 5-L fermenter using batch and fed-batch fermentation. B. subtilis PncB1-PnuC achieved an NMN titer of 3,398 mg/L via fed-batch fermentation and glucose supplementation, which was 30.72% higher than that achieved via batch fermentation.

Discussion

This study provides a safe and economical approach for producing NMN on an industrial scale.

Systematic Engineering of Escherichia coli for Efficient Production of Pseudouridine from Glucose and Uracil

In this study, we proposed a biological approach to efficiently produce pseudouridine (Ψ) from glucose and uracil in vivo using engineered Escherichia coli. By screening host strains and core enzymes, E. coli MG1655 overexpressing Ψ monophosphate (ΨMP) glycosidase and ΨMP phosphatase was obtained, which displayed the highest Ψ concentration. Then, optimization of the RBS sequences, enhancement of ribose 5-phosphate supply in the cells, and overexpression of the membrane transport protein UraA were investigated. Finally, fed-batch fermentation of Ψ in a 5 L fermentor can reach 27.5 g/L with a yield of 89.2 mol % toward uracil and 25.6 mol % toward glucose within 48 h, both of which are the highest to date. In addition, the Ψ product with a high purity of 99.8% can be purified from the fermentation broth after crystallization. This work provides an efficient and environmentally friendly protocol for allowing for the possibility of Ψ bioproduction on an industrial scale.

Role and Potential Mechanisms of Nicotinamide Mononucleotide in Aging

Nicotinamide adenine dinucleotide (NAD+) has recently attracted much attention due to its role in aging and lifespan extension. NAD+ directly and indirectly affects many cellular processes, including metabolic pathways, DNA repair, and immune cell activities. These mechanisms are critical for maintaining cellular homeostasis. However, the decline in NAD+ levels with aging impairs tissue function, which has been associated with several age-related diseases. In fact, the aging population has been steadily increasing worldwide, and it is important to restore NAD+ levels and reverse or delay these age-related disorders. Therefore, there is an increasing demand for healthy products that can mitigate aging, extend lifespan, and halt age-related consequences. In this case, several studies in humans and animals have targeted NAD+ metabolism with NAD+ intermediates. Among them, nicotinamide mononucleotide (NMN), a precursor in the biosynthesis of NAD+, has recently received much attention from the scientific community for its anti-aging properties. In model organisms, ingestion of NMN has been shown to improve age-related diseases and probably delay death. Here, we review aspects of NMN biosynthesis and the mechanism of its absorption, as well as potential anti-aging mechanisms of NMN, including recent preclinical and clinical tests, adverse effects, limitations, and perceived challenges.

Biosynthesis of Nicotinamide Mononucleotide: Synthesis Method, Enzyme, and Biocatalytic System

Nicotinamide mononucleotide (NMN) has garnered substantial interest as a functional food product. Industrial NMN production relies on chemical methods, facing challenges in separation, purification, and regulatory complexities, leading to elevated prices. In contrast, NMN biosynthesis through fermentation or enzyme catalysis offers notable benefits like eco-friendliness, recyclability, and efficiency, positioning it as a primary avenue for future NMN synthesis. Enzymatic NMN synthesis encompasses the nicotinamide-initial route and nicotinamide ribose-initial routes. Key among these is nicotinamide riboside kinase (NRK), pivotal in the latter route. The NRK-mediated biosynthesis is emerging as a prominent trend due to its streamlined route, simplicity, and precise specificity. The essential aspect is to obtain an engineered NRK that exhibits elevated activity and robust stability. This review comprehensively assesses diverse NMN synthesis methods, offering valuable insights into efficient, sustainable, and economical production routes. It spotlights the emerging NRK-mediated biosynthesis pathway and its significance. The establishment of an adenosine triphosphate (ATP) regeneration system plays a pivotal role in enhancing NMN synthesis efficiency through NRK-catalyzed routes. The review aims to be a reference for researchers developing green and sustainable NMN synthesis, as well as those optimizing NMN production.

Improvement of an enzymatic cascade synthesis of nicotinamide mononucleotide via protein engineering and reaction-process reinforcement

Enzymatic synthesis of β-nicotinamide mononucleotide (NMN) from D-ribose has garnered widespread attention due to its cheap material, the use of mild reaction conditions, and the ability to produce highly pure products with the desired optical properties. However, the overall NMN yield of this method is impeded by the low activity of rate-limiting enzymes. The ribose-phosphate diphosphokinase (PRS) and nicotinamide phosphoribosyltransferase (NAMPT), that control the rate of the reaction, were engineered to improve the reaction efficacy. The actives of mutants PRS-H150Q and NAMPT-Y15S were 334% and 57% higher than that of their corresponding wild-type enzymes, respectively. Furthermore, by adding pyrophosphatase, the byproduct pyrophosphate which can inhibit the activity of NAMPT was degraded, leading to a 6.72% increase in NMN yield. Following with reaction-process reinforcement, a high yield of 8.10 g L-1 NMN was obtained after 3 h of reaction, which was 56.86-fold higher than that of the stepwise reaction synthesis (0.14 g L-1 ), indicating that the in vitro enzymatic synthesis of NMN from D-ribose and niacinamide is an economical and feasible route.

A holistic approach for process intensification of nicotinamide mononucleotide production via high cell density cultivation under exponential feeding strategy

Nicotinamide mononucleotide (NMN) subsists in all living organisms and has drawn tremendous attention as a nutraceutical and pharmaceutical product for several diseases such as Alzheimer's, cancer, aging, and vascular dysfunction. Here, NMN was produced intracellularly in a high cell density bioreactor using an engineered Escherichiacoli strain via exponential feeding of co-substrates. Fed-batch culture via exponential feeding of co-substrate (glucose) and continuous feeding of substrate (nicotinamide) were performed using different cumulative nicotinamide concentrations. The highest concentration of 19.3 g/L NMN with a dry cell weight of 117 g/L was acquired from a cumulative nicotinamide concentration of 7.2 g/L with a conversion of 98 % from nicotinamide in 28 h. Further, liquid chromatography-mass spectrometry analysis validated the NMN production. This approach will be beneficial in achieving simultaneously low cost and ensuring high quality and quantity of NMN production.

Semirational engineering of Cytophaga hutchinsonii polyphosphate kinase for developing a cost-effective, robust, and efficient adenosine 5'-triphosphate regeneration system

IMPORTANCE

The adenosine 5'-triphosphate (ATP) regeneration system can significantly reduce the cost of many biocatalytic processes. Numerous studies have endeavored to utilize the ATP regeneration system based on Cytophaga hutchinsonii PPK (ChPPK). However, the wild-type ChPPK enzyme possesses limitations such as low enzymatic activity, poor stability, and limited substrate tolerance, impeding its application in catalytic reactions. To enhance the performance of ChPPK, we employed a semi-rational design approach to obtain the variant ChPPK/A79G/S106C/I108F/L285P. The enzymatic kinetic parameters and the catalytic performance in the synthesis of nicotinamide mononucleotide demonstrated that the variant ChPPK/A79G/S106C/I108F/L285P exhibited superior enzymatic properties than the wild-type enzyme. All data indicated that our engineered ATP regeneration system holds inherent potential for implementation in biocatalytic processes.

Metabolic Engineering of Escherichia coli for Efficient Production of Pseudouridine

Pseudouridine-incorporated mRNA vaccines can enhance protein expression and reduce immunogenicity, leading to a high demand for pseudouridine to be used in mRNA drug production. To achieve the low-cost production of pseudouridine, Escherichia coli was systematically modified to utilize inexpensive raw materials to efficiently produce pseudouridine. First, in the pyrimidine biosynthesis pathway, genes related to the precursor competing pathway and the negative regulator were deleted, which increased pseudouridine production. Second, two critical genes, pseudouridine-5'-phosphate glycosidase (psuG) and phosphatase genes from different bacteria, were screened and employed in various genetic constructs, and the pseudouridine yield of the optical strain increased to 599 mg/L. The accumulation of pseudouridine was further increased by the deletion of pseudouridine catabolism-related genes. Ultimately, the pseudouridine titer in a 5 L bioreactor reached 7.9 g/L, and the yield of pseudouridine on glucose was 0.15 g/g. Overall, a cell factory producing pseudouridine was successfully constructed and showed potential for industrial production.

Synthesis of NMN by cascade catalysis of intracellular multiple enzymes

β-Nicotinamide mononucleotide is a biologically active nucleotide compound, and its excellent anti-aging activity is widely used in medicine and has multiple functions, making NMN have broad application prospects in the fields of nutrition, health food, and even medicine. Herein, based on the supply of the co-substrate PRPP, we designed and constructed three in vivo NMN synthesis pathways using glucose, xylose, and arabinose as raw materials and Escherichia coli as the host. The best in vivo pathway through whole-cell catalysis was identified. Then, we optimized the cell culture and catalytic conditions of the optimal path to determine the optimal conditions and ultimately obtained an NMN titer of 1.8 mM.

Technology and functional insights into the nicotinamide mononucleotide for human health

Nicotinamide mononucleotide (NMN), a naturally occurring biologically active nucleotide, mainly functions via mediating the biosynthesis of NAD⁺. In recent years, its excellent pharmacological activities including anti-aging, treating neurodegenerative diseases, and protecting the heart have attracted increasing attention from scholars and entrepreneurs for production of a wide range of formulations, including functional food ingredients, health care products, active pharmaceuticals, and pharmaceutical intermediates. Presently, the synthesis methods of NMN mainly include two categories: chemical synthesis and biosynthesis. With the development of biocatalyst engineering and synthetic biology strategies, bio-preparation has proven to be efficient, economical, and sustainable methods. This review summarizes the chemical synthesis and biosynthetic pathways of NMN and provides an in-depth investigation on the mining and modification of enzyme resources during NMN biosynthesis, as well as the screening of hosts and optimization of chassis cells via metabolic engineering, which provide effective strategies for efficient production of NMN. In addition, an overview of the significant physiological functions and activities of NMN is elaborated. Finally, future research on technical approaches to further enhance NMN synthesis and strengthen clinical studies of NMN are prospected, which would lay the foundation for further promoting the application of NMN in nutrition, healthy food, and medicine in the future. KEY POINTS: • NMN supplementation effectively increases the level of NAD⁺. • The chemical and biological synthesis of NMN are comprehensively reviewed. • The impact of NMN on the treatment of various diseases is summarized.

Enhancement of phycocyanobilin biosynthesis in Escherichia coli by strengthening the supply of precursor and artificially self-assembly complex

Phycocyanobilin (PCB) is widely used in healthcare, food processing, and cosmetics. Escherichia coli is the common engineered bacterium used to produce PCB. However, it still suffers from low production level, precursor deficiency, and low catalytic efficiency. In this study, a highly efficient PCB-producing strain was created. First, chassis strains and enzyme sources were screened, and copy numbers were optimized, affording a PCB titer of 9.1 mg/L. Most importantly, the rate-limiting steps of the PCB biosynthetic pathway were determined, and the supply of precursors necessary for PCB synthesis was increased from endogenous sources, affording a titer of 21.4 mg/L. Then, the key enzymes for PCB synthesis, HO1 and PcyA, were assembled into a multi-enzyme complex using the short peptide tag RIAD-RIDD, and 23.5 mg/L of PCB was obtained. Finally, the basic conditions for PCB fermentation were initially determined in 250 mL shake flasks and a 5-L bioreactor to obtain higher titers of PCB. The final titer of PCB reached 147.0 mg/L, which is the highest reported titer of PCB so far. This research provided the foundation for the industrial production of PCB and its derivatives.

Systematic engineering of Escherichia coli for efficient production of nicotinamide riboside from nicotinamide and 3-cyanopyridine

Nicotinamide riboside (NR), a key biosynthetic precursor of NAD⁺, is receiving increasing attention because of its role. In this study, a whole-cell catalysis method to efficiently synthesize NR was established. First, the performance of 5'-nucleotidase (UshA) from Escherichia coli was confirmed to have high catalytic activity to synthesize NR. Then, the endogenous NR degradation pathway was detected, and the genes (rihA, rihB, and rihC) involved in NR degradation were knocked out, which enabled NR biosynthesis. In addition, the important role of the signal peptide of UshA in NR transport had been confirmed. Subsequently, nitrile hydratase was introduced to achieve the conversion of 3-cyanopyridine to NR. Finally, the NR titer reached 25.6 and 29.8 g/L with nicotinamide and 3-cyanopyridine, respectively, as substrates in a 5-L bioreactor, the efficient biosynthesis of NR in E. coli by using nicotinamide and 3-cyanopyridine.

Rapid prototyping enzyme homologs to improve titer of nicotinamide mononucleotide using a strategy combining cell-free protein synthesis with split GFP

Engineering biological systems to test new pathway variants containing different enzyme homologs is laborious and time-consuming. To tackle this challenge, a strategy was developed for rapidly prototyping enzyme homologs by combining cell-free protein synthesis (CFPS) with split green fluorescent protein (GFP). This strategy featured two main advantages: (1) dozens of enzyme homologs were parallelly produced by CFPS within hours, and (2) the expression level and activity of each homolog was determined simultaneously by using the split GFP assay. As a model, this strategy was applied to optimize a 3-step pathway for nicotinamide mononucleotide (NMN) synthesis. Ten enzyme homologs from different organisms were selected for each step. Here, the most productive homolog of each step was identified within 24 h rather than weeks or months. Finally, the titer of NMN was increased to 1213 mg/L by improving physiochemical conditions, tuning enzyme ratios and cofactor concentrations, and decreasing the feedback inhibition, which was a more than 12-fold improvement over the initial setup. This strategy would provide a promising way to accelerate design-build-test cycles for metabolic engineering to improve the production of desired products.

High level expression of nicotinamide nucleoside kinase from Saccharomyces cerevisiae and its purification and immobilization by one-step method

Nicotinamide riboside kinase (NRK) plays an important role in the synthesis of β -nicotinamide nucleotide (NMN). NMN is a key intermediate of NAD+ synthesis, and it actually contribute to the well-being of our health. In this study, gene mining technology was used to clone nicotinamide nucleoside kinase gene fragments from S. cerevisiae, and the ScNRK1 was achieved a high level of soluble expression in E. coli BL21. Then, the reScNRK1 was immobilized by metal affinity label to optimize the enzyme performance. The results showed that the enzyme activity in the fermentation broth was 14.75 IU/mL, and the specific enzyme activity after purification was 2252.59 IU/mg. After immobilization, the optimum temperature of the immobilized enzyme was increased by 10°C compared with the free enzyme, and the temperature stability was improved with little change in pH. Moreover, the activity of the immobilized enzyme remained above 80% after four cycles of immobilized reScNRK1, which makes the enzyme more advantageous in the enzymatic synthesis of NMN.

Dual-channel glycolysis balances cofactor supply for l-homoserine biosynthesis in Corynebacterium glutamicum

l-Homoserine is an important platform compound that is widely used to produce many valuable bio-based products, but production of l-homoserine in Corynebacterium glutamicum remains low. In this study, an efficient l-homoserine-producing strain was constructed. Native pentose phosphate pathway (PPP) was enhanced and heterologous Entner-Doudoroff (ED) pathway was carefully introduced into l-homoserine-producing strain, which increased the l-homoserine titer. Coexpression of NADH-dependent aspartate-4-semialdehyde dehydrogenase and aspartate dehydrogenase could increase the titer from 11.3 to 13.3 g/L. Next, NADP⁺-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP-GPD) was coexpressed with that of NAD⁺-dependent (NAD-GPD) to construct dual-channel glycolysis for balance of intracellular cofactors, which increased the l-homoserine titer by 48.6 % to 16.8 g/L. Finally, engineered strain Cg18-1 accumulated 63.5 g/L l-homoserine after 96 h in a 5 L bioreactor, the highest titer reported to date for C. glutamicum. This dual-channel glycolysis strategy provides a reference for automatic cofactor regulation to promote efficient biosynthesis of other target products.