High-Yield Synthesis of 2'-Fucosyllactose from Glycerol and Glucose in Engineered Escherichia coli

Efficient production of 2'-fucosyllactose in Pichia pastoris through metabolic engineering and constructing an orthogonal energy supply system

2'-fucosyllactose (2'-FL) holds significant role in the infants' nutrition. While microbial production of 2'-FL has predominantly utilized Escherichia coli and Saccharomyces cerevisiae, the potential of Pichia pastoris, renowned for its robust NADPH regeneration capability, remains underexplored. Herein, we systematically engineered the metabolism of P. pastoris to develop an efficient 2'-FL-producing cell factory. We first constructed the de novo biosynthesis pathway for 2'-FL in P. pastoris, achieving an initial titer of 0.143 g/L. By optimizing enzyme selection and solubility of α-1,2-fucosyltransferase (FutC), 2'-FL production was enhanced by nearly ten folds. Subsequently, engineering NADPH supply further increased the 2'-FL production by 170 %. Furthermore, we enhanced energy supply by incorporating an orthogonal energy module based on the methanol dissimilation pathway and increasing GTP availability, resulting in a 32 % improvement in 2'-FL production. Finally, through the optimization of fermentation condition, we realized the production titer of 2'-FL to 3.50 g/L in shake-flask, representing the highest titer in P. pastoris. These findings highlight the potential of P. pastoris as a chassis to produce chemicals by providing abundant NADPH and utilizing methanol as co-substrate to supply sufficient energy.

Engineering Pichia pastoris for Efficient De Novo Synthesis of 2'-Fucosyllactose

2'-Fucosyllactose (2'-FL), the most abundant in human milk oligosaccharides (HMOs), is a nutrient of great importance. As a safe organism widely used in industries, Pichia pastoris was tested here for 2'-FL production. The de novo biosynthesis pathway of 2'-FL was constructed using genome-editing technology based on CRISPR-Cas9 with an initial titer of 1.01 g/L. Introducing N-terminal SUMO or Ub tag to FucT2 and the transporter CDT2 from Neurospora crassa into P. pastoris was found to improve 2'-FL production. Then, modular metabolic engineering was conducted to improve 2'-FL production, enhancing the GTP supply module, NADPH regeneration module, and precursor supply module. Subsequently, the key enzyme FucT2 was semirationally designed to further increase 2'-FL production. Finally, the 2'-FL production by engineered P. pastoris was scaled up to the 3 L fermenter in fed-batch mode, resulting in a titer of 22.35 g/L that is the highest by P. pastoris. The results prove the effectiveness of the metabolic engineering strategies and demonstrate that P. pastoris could be a potential chassis to produce HMOs.

Biosynthesis and metabolic engineering of natural sweeteners

Natural sweeteners have attracted widespread attention because they are eco-friendly, healthy, low in calories, and tasty. The demand for natural sweeteners is increasing together with the popularity of green, low-carbon, sustainable development. With the development of synthetic biology, microbial cell factories have emerged as an effective method to produce large amounts of natural sweeteners. This technology has significantly progressed in recent years. This review summarizes the pathways and the enzymes related to the biosynthesis of natural sweeteners, such as mogrosides, steviol glycosides, glycyrrhizin, glycyrrhetinic acid, phlorizin, trilobatin, erythritol, sorbitol, mannitol, thaumatin, monellin, and brazzein. Moreover, it focuses on the research about the microbial production of these natural sweeteners using synthetic biology methods, aiming to provide a reference for future research on the production of natural sweeteners.

Multidimensional Engineering of Escherichia coli MG1655 for the Efficient Biosynthesis of Difucosyllactose

Difucosyllactose (DFL), a representative bisfucosylated oligosaccharide found in human milk, has garnered significant attention due to its immense health benefits. To date, several plasmid-based engineered strains have been established for DFL synthesis. However, these strains face challenges such as antibiotic dependence and plasmid instability, which limit their commercial application in the food industry. For this, plasmid-free Escherichia coli MG1655 strains were established by integrating multicopy numbers of SAMT and fut3Bc into the genome and overexpressing key genes involved in the GDP-l-fucose pathway. To enhance the catalytic efficiency, Fut3Bc was mutated based on AlphaFold 3, obtaining a beneficial mutant Fut3Bc (F24Y). The optimized plasmid-free strain, MGA2S-5, containing 2 copies of SAMT and 4 copies of fut3Bc (F24Y) in the genome was obtained. Eventually, strain MGA2S-5 synthesized 35.04 g/L DFL in a 7 L bioreactor by fed-batch cultivation, with no intermediate products remaining in the medium.

Metabolic Engineering of Escherichia coli BL21(DE3) for 2'-Fucosyllactose Synthesis in a Higher Productivity

2'-Fucosyllactose (2'-FL) is the most abundant human milk oligosaccharides (HMOs). 2'-FL exhibits great benefits for infant health, such as preventing infantile diarrhea and promoting the growth of intestinal probiotics. The microbial cell factory technique has shown promise for the massive production of 2'-FL. Here, we aimed to construct a recombinant E. coli BL21(DE3) strain for the hyperproduction of 2'-FL. Initially, multicopy genomic integration and expression of the lactose permease gene lacY reduced the formation of byproducts. Furthermore, a more efficient Shine-Dalgarno sequence was used to replace the wild-type sequence in the manC-manB and gmd-wcaG gene clusters, which significantly increased the 2'-FL titer. Based on these results, we overexpressed the sugar efflux transporter SetA and knocked out the pgi gene. This further improved 2'-FL synthesis when glycerol was used as the sole carbon source. Finally, a new α-1,2-fucosyltransferase was identified in Neisseria sp., which exhibited a higher capacity for 2'-FL production. Fed-batch fermentation produced 141.27 g/L 2'-FL in 45 h with a productivity of 3.14 g/L × h. This productivity rate achieved the highest recorded 2'-FL levels, indicating the potential of engineered E. coli BL21 (DE3) strains for use in the industrial production of 2'-FL.

Enhancement of the yield of poly (ethylene terephthalate) hydrolase production using cell membrane protection strategy

Biodegradation, particularly via enzymatic degradation, has emerged as an efficient and eco-friendly solution for Poly (ethylene terephthalate) (PET) pollution. The production of PET hydrolases plays a role in the large-scale enzymatic degradation. However, an effective variant, 4Mz, derived from Thermobifida fusca cutinase (Tfu_0883), was previously associated with a significant reduction in yield when compared to the wild-type enzyme. In this study, a novel cell membrane protection strategy was developed to enhance the yield of 4Mz. This approach increased the yield of 4Mz by 18.2-fold from shaken flasks to 3-L bioreactors, reaching a yield of 3.1 g·L-1, the highest yield of a PET hydrolase described thus far. In addition, the raw culture broth from 4Mz was applied directly for the enzymatic degradation of PET bottles, achieving a 91.2 % degradation rate. These advancements render the large-scale enzymatic degradation of PET more feasible, thus contributing to the more sustainable management of plastic waste.

Metabolic engineering of Priestia megaterium for 2'-fucosyllactose production

BACKGROUND

2'-Fucosyllactose (2'-FL) is a predominant human milk oligosaccharide that significantly enhances infant nutrition and immune health. This study addresses the need for a safe and economical production of 2'-FL by employing Generally Recognized As Safe (GRAS) microbial strain, Priestia megaterium ATCC 14581. This strain was chosen for its robust growth and established safety profile and attributing suitable for industrial-scale production.

RESULTS

The engineering targets included the deletion of the lacZ gene to prevent lactose metabolism interference, introduction of α-1,2-fucosyltransferase derived from the non-pathogenic strain, and optimization of the GDP-L-fucose biosynthesis pathway through the overexpression of manA and manC. These changes, coupled with improvements in lactose uptake and utilization through random mutagenesis, led to a high 2'-FL yield of 28.6 g/L in fed-batch fermentation, highlighting the potential of our metabolic engineering strategies on P. megaterium.

CONCLUSIONS

The GRAS strain P. megaterium ATCC 14581 was successfully engineered to overproduce 2'-FL, a valuable human milk oligosaccharide, through a series of genetic modifications and metabolic pathway optimizations. This work underscores the feasibility of using GRAS strains for the production of oligosaccharides, paving the way for safer and more efficient methods in biotechnological applications. Future studies could explore additional genetic modifications and optimization of fermentation conditions of the strain to further enhance 2'-FL yield and scalability.

Metabolic engineering of Escherichia coli for upcycling of polyethylene terephthalate waste to vanillin

Polyethylene terephthalate (PET) waste presents a significant environmental challenge due to its durability and resistance to degradation. Innovative approaches for upcycling PET waste into high-value chemicals can mitigate these issues while contributing to a circular economy. In this study, we developed a multi-enzyme cascade system in E. coli to convert PET-derived monomer terephthalic acid (TPA) into vanillin (VAN). The metabolic engineering approach was then employed to increase VAN production, including 1) inhibition of VAN degradation by knocking out endogenous aldehyde reductases and alcohol dehydrogenases and 2) enhancement of TPA uptake by modifying membrane proteins to increase cell permeability. The engineered E. coli demonstrated a VAN production of 658.55 mg/L from 1992 mg/L of TPA with a molar conversion rate of 71.1 %, representing the highest production of VAN using TPA as the substrate. Additionally, the engineered E. coli effectively converted post-consumer PET waste into VAN under mild conditions, with the highest production of 259.2 mg/L in 20× diluted PET hydrolysates, highlighting its potential for application in PET waste upcycling. This approach not only provides an environmentally friendly alternative to traditional chemical synthesis but also offers substantial economic benefits by transforming low-value waste into high-value chemicals.

Construction of an engineered Escherichia coli for effective synthesis of 2'-fucosyllactose via the salvage pathway

2'-Fucosyllactose (2'-FL) is one of the important functional oligosaccharides in breast milk. So far, few attempts on biosynthesis of 2'-FL by the salvage pathway have been reported. Herein, the salvage pathway enzyme genes were introduced into the E. coli BL21star(DE3) for synthesis of 2'-FL. The 2'-FL titer increased from 1.56 to 2.13 g/L by deleting several endogenous genes on competitive pathways. The α-1,2-fucosyltransferase (WbgL) was selected, and improved the 2'-FL titer to 2.88 g/L. Additionally, the expression level of pathway enzyme genes was tuned through optimizing the plasmid copy number. Furthermore, the spatial distribution of WbgL was enhanced by fusing with the MinD C-tag. After optimizing the fermentation conditions, the 2'-FL titer reached to 7.13 g/L. The final strain produced 59.22 g/L of 2'-FL with 95% molar conversion rate of lactose and 92% molar conversion rate of fucose in a 5 L fermenter. These findings will contribute to construct a highly efficient microbial cell factory to produce 2'-FL or other HMOs.

Microbial Synthesis of Lacto-N-fucopentaose I with High Titer and Purity by Screening of Specific Glycosyltransferase and Elimination of Residual Lacto-N-triose II and Lacto-N-tetraose

Lacto-N-fucopentaose I (LNFP I) has recently been approved as generally recognized as safe, demonstrating its great commercial potential in the food industry. Microbial synthesis through metabolic engineering strategies is an effective approach for large-scale production of LNFP I. Biosynthesis of LNFP I requires consideration of two key points: high titer with low byproduct 2'-fucosyllactose (2'-FL) generation and high purity with low lacto-N-triose II (LNTri II) and lacto-N-tetraose (LNT) residues. Herein, α1,2-fucosyltransferase from Thermoanaerobacterium sp. RBIITD was screened from 16 selected LNFP I-producing glycosyltransferase candidates, showing the highest in vivo LNFP I productivity. Chromosomal integration of wbgO enhanced the LNFP I production by improving the precursor conversion from LNTri II to LNT. The best engineered strain produced 4.42 and 35.1 g/L LNFP I in shake-flask and fed-batch cultivation, respectively. The residual LNTri II and LNT were eliminated by further cultivation with a recombinant strain coexpressing Bifidobacterium bifidum β-N-acetylhexosaminidase and lacto-N-biosidase. A strategy for LNFP I biosynthesis with high yield and purity was finally realized, providing support for its practical application in large-scale production.