Production of human milk oligosaccharides by enzymatic and whole-cell microbial biotransformations

Heterologous expression of a novel galactose-1-phosphate uridylyltransferase from Thermodesulfatator indicus and its application for bioproduction of Gal-β-1,4-GlcNAc-X

Nucleotide sugars (UDP-Sugars) are essential for the production of polysaccharides and glycoconjugates utilized in medicines, cosmetics, and food industries. The enzyme Galactose-1-phosphate uridylyltransferase (GalU; EC 2.7.7.12) is responsible for the synthesis of UDP-galactose from α-d-galactose-1-phosphate (Gal-1P) and UTP. A novel bacterial GalU (TiGalU) encoded from a thermophilic bacterium, Thermodesulfatator indicus, was successfully purified using the Ni-NTA column after being expressed in Escherichia coli. The optimal pH for recombinant TiGalU was determined to be 5.5. The optimum temperature of the enzyme was 45 °C. The activity of TiGalU was not dependent on Mg2+ and was strongly inhibited by SDS. When coupled with galactose kinase (GALK1) and β-1,4-galactosyltransferase 1 (B4GALT1), the enzyme enabled the one-pot synthesis of Gal-β-1,4-GlcNAc-X by utilizing galactose and UTP as substrates. This study reported the in vitro biosynthesis of Gal-β-1,4-GlcNAc-X for the first time, providing an environmentally friendly way to biosynthesis glycosides and other polysaccharides.

Modifiable and Non-Modifiable Factors That Affect Human Milk Oligosaccharides Composition

Human milk, the gold standard in infant nutrition, is a unique fluid that provides essential nutrients such as lactose, lipids, proteins, and free oligosaccharides. While its primary role is nutritional, it also protects against pathogens. This protection mainly comes from immunoglobulins, with human milk oligosaccharides (HMOs) providing additional support by inhibiting pathogen binding to host cell ligands. The prebiotic and immune-modulatory activity of HMOs strongly depends on their structure. Over 200 individual structures have been identified so far, with the composition varying significantly among women. The structure and composition of HMOs are influenced by factors such as the Lewis blood group, secretor status, and the duration of nursing. HMO profiles are heavily influenced by maternal phenotypes, which are defined based on the expression of two specific fucosyltransferases. However, recent data have shown that HMO content can be modified by various factors, both changeable and unchangeable, including diet, maternal age, gestational age, mode of delivery, breastfeeding frequency, and race. The first part of this overview presents the historical background of these sugars and the efforts by scientists to extract them using the latest chromatography methods. The second part is divided into subchapters that examine modifiable and non-modifiable factors, reviewing the most recent articles on HMO composition variations due to specific reasons and summarizing potential future challenges in conducting these types of studies.

Co-immobilization of a bi-enzymatic cascade into hierarchically porous MIL-53 for efficient 6'-sialyllactose production

6'-Sialyllactose (6'-SL), the most abundant sialylated human milk oligosaccharide, has attracted attention for its potential application in supplementary infant formulas. Herein, we report a facile strategy to construct a cascade bioreactor for the enzymatic synthesis of 6'-SL by co-immobilizing an enzymatic module consisting of CMP-sialic acid synthase and α-2,6-sialyltransferase into hierarchically porous MIL-53 (HP-MIL-53). The as-prepared HP-MIL-53 showed high enzyme immobilization capacity, reaching 226 mg g-1. Furthermore, the co-immobilized enzymes exhibited higher initial catalytic efficiency, and thermal, pH and storage stability than the free ones. Finally, the 6'-SL yield remained >80% after 13 cycles of use. We expect that HP-MIL-53 would have potential industrial applications in the enzymatic modular synthesis of 6'-SL and other glycans.

Guide RNA structure design enables combinatorial CRISPRa programs for biosynthetic profiling

Engineering metabolism to efficiently produce chemicals from multi-step pathways requires optimizing multi-gene expression programs to achieve enzyme balance. CRISPR-Cas transcriptional control systems are emerging as important tools for programming multi-gene expression, but poor predictability of guide RNA folding can disrupt expression control. Here, we correlate efficacy of modified guide RNAs (scRNAs) for CRISPR activation (CRISPRa) in E. coli with a computational kinetic parameter describing scRNA folding rate into the active structure (rS = 0.8). This parameter also enables forward design of scRNAs, allowing us to design a system of three synthetic CRISPRa promoters that can orthogonally activate (>35-fold) expression of chosen outputs. Through combinatorial activation tuning, we profile a three-dimensional design space expressing two different biosynthetic pathways, demonstrating variable production of pteridine and human milk oligosaccharide products. This RNA design approach aids combinatorial optimization of metabolic pathways and may accelerate routine design of effective multi-gene regulation programs in bacterial hosts.

Enzymatic modular synthesis of asymmetrically branched human milk oligosaccharides

Human milk oligosaccharides (HMOs) are intricate glycans that promote healthy growth of infants and have been incorporated into infant formula as food additives. Despite their importance, the limited availability of asymmetrically branched HMOs hinders the exploration of their structure and function relationships. Herein, we report an enzymatic modular strategy for the efficient synthesis of these HMOs. The key branching enzyme for the assembly of branched HMOs, human β1,6-N-acetylglucosaminyltransferase 2 (GCNT2), was successfully expressed in Pichia pastoris for the first time. Then, it was integrated with six other bacterial glycosyltransferases to establish seven glycosylation modules. Each module comprises a one-pot multi-enzyme (OPME) system for in-situ generation of costly sugar nucleotide donors, combined with a glycosyltransferase for specific glycosylation. This approach enabled the synthesis of 31 branched HMOs and 13 linear HMOs in a stepwise manner with well-programmed synthetic routes. The binding details of these HMOs with related glycan-binding proteins were subsequently elucidated using glycan microarray assays to provide insights into their biological functions. This comprehensive collection of synthetic HMOs not only serves as standards for HMOs structure identification in complex biological samples but also significantly enhances the fields of HMOs glycomics, opening new avenues for biomedical applications.

Automated chemoenzymatic modular synthesis of human milk oligosaccharides on a digital microfluidic platform

Glycans, along with proteins, nucleic acids, and lipids, constitute the four fundamental classes of biomacromolecules found in living organisms. Generally, glycans are attached to proteins or lipids to form glycoconjugates that perform critical roles in various biological processes. Automatic synthesis of glycans is essential for investigation into structure-function relationships of glycans. In this study, we presented a method that integrated magnetic bead-based manipulation and modular chemoenzymatic synthesis of human milk oligosaccharides (HMOs), on a DMF (Digital Microfluidics) platform. On the DMF platform, enzymatic modular reactions were conducted in solution, and purification of products or intermediates was achieved by using DEAE magnetic beads, circumventing the intricate steps required for traditional solid-phase synthesis. With this approach, we have successfully synthesized eleven HMOs with highest yields of up to >90% on the DMF platform. This study would not only lay the foundation for OPME synthesis of glycans on the DMF platform, but also set the stage for developing automated enzymatic glycan synthesizers based on the DMF platform.

Improved Enzymatic Production of the Fucosylated Human Milk Oligosaccharide LNFP II with GH29B α-1,3/4-l-Fucosidases

Five GH29B α-1,3/4-l-fucosidases (EC 3.2.1.111) were investigated for their ability to catalyze the formation of the human milk oligosaccharide lacto-N-fucopentaose II (LNFP II) from lacto-N-tetraose (LNT) and 3-fucosyllactose (3FL) via transglycosylation. We studied the effect of pH on transfucosylation and hydrolysis and explored the impact of specific mutations using molecular dynamics simulations. LNFP II yields of 91 and 65% were obtained for the wild-type SpGH29C and CpAfc2 enzymes, respectively, being the highest LNFP II transglycosylation yields reported to date. BbAfcB and BiAfcB are highly hydrolytic enzymes. The results indicate that the effects of pH and buffer systems are enzyme-dependent yet relevant to consider when designing transglycosylation reactions. Replacing Thr284 in BiAfcB with Val resulted in increased transglycosylation yields, while the opposite replacement of Val258 in SpGH29C and Val289 CpAfc2 with Thr decreased the transfucosylation, confirming a role of Thr and Val in controlling the flexibility of the acid/base loop in the enzymes, which in turn affects transglycosylation. The substitution of an Ala residue with His almost abolished secondary hydrolysis in CpAfc2 and BbAfcB. The results are directly applicable in the enhancement of transglycosylation and may have significant implications for manufacturing of LNFP II as a new infant formula ingredient.

High-Yield Synthesis of Lacto-N-Neotetraose from Glycerol and Glucose in Engineered Escherichia coli

Lacto-N-neotetraose (LNnT) is a neutral human milk oligosaccharide with important biological functions. However, the low LNnT productivity and the incomplete conversion of the intermediate lacto-N-tetraose II (LNT II) currently limited the sustainable biosynthesis of LNnT. First, the LNnT biosynthetic module was integrated in Escherichia coli. Next, the LNnT export system was optimized to alleviate the inhibition of intracellular LNnT synthesis. Furthermore, by utilizing rate-limiting enzyme diagnosis, the expressions of LNnT synthesis pathway genes were finely regulated to further enhance the production yield of LNnT. Subsequently, a strategy of cofermentation using a glucose/glycerol (4:6, g/g) mixed feed was employed to regulate carbon flux distribution. Finally, by overexpressing key transferases, LNnT and LNT II titers reached 112.47 and 7.42 g/L, respectively, in a 5 L fermenter, and 107.4 and 2.08 g/L, respectively, in a 1000 L fermenter. These are the highest reported titers of LNnT to date, indicating its significant potential for industrial production.

Antimicrobial Properties of Colostrum and Milk

The growing number of antibiotic resistance genes is putting a strain on the ecosystem and harming human health. In addition, consumers have developed a cautious attitude towards chemical preservatives. Colostrum and milk are excellent sources of antibacterial components that help to strengthen the immunity of the offspring and accelerate the maturation of the immune system. It is possible to study these important defenses of milk and colostrum, such as lactoferrin, lysozyme, immunoglobulins, oligosaccharides, etc., as biotherapeutic agents for the prevention and treatment of numerous infections caused by microbes. Each of these components has different mechanisms and interactions in various places. The compound's mechanisms of action determine where the antibacterial activity appears. The activation of the antibacterial activity of milk and colostrum compounds can start in the infant's mouth during lactation and continue in the gastrointestinal regions. These antibacterial properties possess potential for therapeutic uses. In order to discover new perspectives and methods for the treatment of bacterial infections, additional investigations of the mechanisms of action and potential complexes are required.

Determination of Seven Human Milk Oligosaccharides (HMOs) in Infant Formula and Adult Nutritionals: First Action 2022.07

BACKGROUND

Human milk oligosaccharides (HMOs) are important components of breast milk and may be responsible for some of the benefits of breastfeeding, including resistance to infections and the development of a healthy gut microbiota. Selected HMOs are now available for addition to infant formula, and suitable methods to control the dosing rate are needed.

OBJECTIVE

To develop and validate a suitable method for the analysis of HMOs in infant formula.

METHOD

A method was developed for the determination of seven human milk oligosaccharides (2'-fucosyllactose, 3-fucosyllactose, 3'-sialyllactose, 6'-sialyllactose (6'SL), 2',3-difucosyllactose, lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT)) in infant formula and adult nutritionals. The oligosaccharides are labeled at their reducing end with 2-aminobenzamide, separated by liquid chromatography and detected using a fluorescence detector. Maltodextrins are enzymatically hydrolyzed before analysis to prevent potential interference; likewise, an optional β-galactosidase treatment can be used to remove β-galactooligosaccharides. Fructooligosaccharides or polydextrose do not generally interfere with the analysis.

RESULTS

The method has been validated in a single laboratory on infant formula and adult nutritionals. The seven HMOs were spiked into eight matrixes at three or four spike levels, giving a total of 176 data points. Recoveries were in the range of 90.9-109% in all cases except at the lowest spike level in one matrix (elemental formula), where the LNT recovery was 113%, the LNnT recovery was 111%, and the 6'SL recovery was 121%. Relative repeatabilities (RSD(r)) were in the range of 0.1-4.2%. The performance is generally within the requirements outlined in the Standard Method Performance Requirements (SMPR®) published by AOAC INTERNATIONAL.

CONCLUSIONS

The method developed is suitable for the determination of seven HMOs in infant formula and demonstrated good performance during single-laboratory validation.

HIGHLIGHTS

A method has been developed that is suitable for the determination of seven HMOs in infant formula.

Strategies for Automated Enzymatic Glycan Synthesis (AEGS)

Glycans are the most abundant biopolymers on earth and are constituents of glycoproteins, glycolipids, and proteoglycans with multiple biological functions. The availability of different complex glycan structures is of major interest in biotechnology and basic research of biological systems. High complexity, establishment of general and ubiquitous synthesis techniques, as well as sophisticated analytics, are major challenges in the development of glycan synthesis strategies. Enzymatic glycan synthesis with Leloir-glycosyltransferases is an attractive alternative to chemical synthesis as it can achieve quantitative regio- and stereoselective glycosylation in a single step. Various strategies for synthesis of a wide variety of different glycan structures has already be established and will exemplarily be discussed in the scope of this review. However, the application of enzymatic glycan synthesis in an automated system has high demands on the equipment, techniques, and methods. Different automation approaches have already been shown. However, while these techniques have been applied for several glycans, only a few strategies are able to conserve the full potential of enzymatic glycan synthesis during the process - economical and enzyme technological recycling of enzymes is still rare. In this review, we show the major challenges towards Automated Enzymatic Glycan Synthesis (AEGS). First, we discuss examples for immobilization of glycans or glycosyltransferases as an important prerequisite for the embedment and implementation in an enzyme reactor. Next, improvement of bioreactors towards automation will be described. Finally, analysis and monitoring of the synthesis process are discussed. Furthermore, automation processes and cycle design are highlighted. Accordingly, the transition of recent approaches towards a universal automated glycan synthesis platform will be projected. To this end, this review aims to describe essential key features for AEGS, evaluate the current state-of-the-art and give thought- encouraging impulses towards future full automated enzymatic glycan synthesis.

Human milk oligosaccharide lacto-N-tetraose: Physiological functions and synthesis methods

Human milk oligosaccharides (HMOs) have attracted considerable attention due to their unique role in boosting infant health. Among the HMOs, lacto-N-tetraose (LNT) is a significant constituent associated with various health benefits, such as prebiotic effects, antiadhesive antimicrobials, antiviral protection, and immune modulators. LNT has received a "Generally Recognized as Safe" status by the American Food and Drug Administration and was approved as a food ingredient for infant formula. However, the limited availability of LNT poses a major challenge for its application in food and medicine. In this review, we first explored the physiological functions of LNT. Next, we describe several synthesis methods for production of LNT, including chemical, enzymatic, and cell factory approaches, and summarize the pivotal research results. Finally, challenges and opportunities for the large-scale synthesis of LNT were discussed.

Metabolic Engineering of Escherichia coli for High-Level Production of Lacto-N-neotetraose and Lacto-N-tetraose

Lacto-N-neotetraose (LNnT) and lacto-N-tetraose (LNT) are important oligosaccharides found in breast milk and are commonly used as nutritional supplements in infant formula. We used metabolic engineering techniques to optimize the modified Escherichia coli BL21 star (DE3) strain for efficient synthesis of LNnT and LNT using β-1,4-galactosyltransferase (HpgalT) from Helicobacter pylori and β-1,3-galactosyltransferase (SewbdO) from Salmonella enterica subsp. salamae serovar, respectively. Further, we optimized the expression of three key genes, lgtA, galE, and HpgalT (SewbdO), to synthesize LNnT or LNT and deleted several genes (ugd, ushA, agp, wcaJ, otsA, and wcaC) to block competition in the UDP-galactose synthesis pathway. The optimized strain produced LNnT or LNT with a titer of 22.07 or 48.41 g/L, respectively, in a supplemented batch culture, producing 0.41 or 0.73 g/L/h, respectively. The strategies used in this study contribute to the development of cell factories for high-level LNnT and LNT and their derivatives.

Combinatorial metabolic engineering and tolerance evolving of Escherichia coli for high production of 2'-fucosyllactose

2'-Fucosyllactose (2'-FL) is an important functional ingredient of advanced infant formula. Here, Escherichia coli MG1655 was engineered for achieving high 2'-FL production. The expressions of 2'-FL synthesis pathway genes were finely regulated with single or multi copies according to rate-limiting enzyme diagnosis. On this basic, the branch pathway genes were deleted, and the overexpression of the 2'-FL efflux protein SetA and the fructose-1,6-bisphosphatase GlpX were tuned. The resulting strain produced 46.06 ± 1.28 g/L 2'-FL in a 5-L fermenter. Furtherly, adaptive laboratory evolution was conducted. A rpoC gene mutation was obtained which could improve the cell tolerance and the 2'-FL production up to 61.06 ± 1.93 g/L, with the highest productivity of 1.70 g/L/h among E. coli strains by now. Taken together, this work provides a combinatorial strategy to improve 2'-FL accumulation including rational fine-tuning pathway genes expressions and irrational adaptive laboratory evolution. This study should be helpful for constructing high level 2'-FL producers.

Spatial organization of pathway enzymes via self-assembly to improve 2'-fucosyllactose biosynthesis in engineered Escherichia coli

As one of the most abundant components in human milk oligosaccharides, 2'-fucosyllactose (2'-FL) possesses versatile beneficial health effects. Although most studies focused on overexpressing or fine-tuning the expression of pathway enzymes and achieved a striking increase of 2'-FL production, directly facilitating the metabolic flux toward the key intermediate GDP-l-fucose seems to be ignored. Here, multienzyme complexes consisting of sequential pathway enzymes were constructed by using specific peptide interaction motifs in recombinant Escherichia coli to achieve a higher titer of 2'-FL. Specifically, we first fine-tuned the expression level of pathway enzymes and balanced the metabolic flux toward 2'-FL synthesis. Then, two key enzymes (GDP-mannose 4,6-dehydratase and GDP- l-fucose synthase) were self-assembled into enzyme complexes in vivo via a short peptide interaction pair RIAD-RIDD (RI anchoring disruptor-RI dimer D/D domains), resulting in noticeable improvement of 2'-FL production. Next, to further strengthen the metabolic flux toward 2'-FL, three pathway enzymes were further aggregated into multienzyme assemblies by using another orthogonal protein interaction motif (Spycatcher-SpyTag or PDZ-PDZlig). Intracellular multienzyme assemblies remarkably enlarged the flux toward 2'-FL biosynthesis and showed a 2.1-fold increase of 2'-FL production compared with a strain expressing free-floating and unassembled enzymes. The optimally engineered strain EZJ23 accumulated 4.8 g/L 2'-FL in shake flask fermentation and was capable of producing 25.1 g/L 2'-FL by fed-batch cultivation. This work provides novel approaches for further improvement and large-scale production of 2'-FL and demonstrates the effectiveness of spatial assembly of pathway enzymes to improve the production of valuable products in the engineered host strain.

Effects of Human Milk Oligosaccharides in Infant Health Based on Gut Microbiota Alteration

The primary active components of breast milk are human milk oligosaccharides (HMOs). HMOs provide many benefits to infants, including regulating their metabolism, immune system, and brain development. Recent studies have emphasized that HMOs act as prebiotics by the metabolism of intestinal microorganisms to produce short-chain fatty acids, which are crucial for infant development. In addition, HMOs with different structural characteristics can form different microbial compositions. HMOs-induced predominant microbes, including Bifidobacterium infantis, B. bifidum, B. breve, and B. longum, and their metabolites demonstrated pertinent health-promoting properties. Meanwhile, HMOs could also directly reduce the occurrence of diseases through the effects of preventing pathogen infection. In this review, we address the probable function of HMOs inside the HMOs-gut microbiota-infant network, by describing the physiological functions of HMOs and the implications of diet on the HMOs-gut microbiota-infant network.

Multi-level metabolic engineering of Escherichia coli for high-titer biosynthesis of 2'-fucosyllactose and 3-fucosyllactose

Fucosyllactoses (FL), including 2'-fucosyllactose (2'-FL) and 3-fucosyllactose (3-FL), have garnered considerable interest for their value in newborn formula and pharmaceuticals. In this study, an engineered Escherichia coli was developed for high-titer FL biosynthesis by introducing multi-level metabolic engineering strategies, including (1) individual construction of the 2'/3-FL-producing strains through gene combination optimization of the GDP-L-fucose module; (2) screening of rate-limiting enzymes (α-1,2-fucosyltransferase and α-1,3-fucosyltransferase); (3) analysis of critical intermediates and inactivation of competing pathways to redirect carbon fluxes to FL biosynthesis; (4) enhancement of the catalytic performance of rate-limiting enzymes by the RBS screening, fusion peptides and multi-copy gene cloning. The final strains EC49 and EM47 produced 9.36 g/L for 2'-FL and 6.28 g/L for 3-FL in shake flasks with a modified-M9CA medium. Fed-batch cultivations of the two strains generated 64.62 g/L of 2'-FL and 40.68 g/L of 3-FL in the 3-L bioreactors, with yields of 0.65 mol 2'-FL/mol lactose and 0.67 mol 3-FL/mol lactose, respectively. This research provides a viable platform for other high-value-added compounds production in microbial cell factories.

The Potential Role of Human Milk Oligosaccharides in Irritable Bowel Syndrome

Irritable Bowel Syndrome (IBS) is the most common gastrointestinal (GI) disorder in Western populations and therefore a major public health/economic concern. However, despite extensive research, psychological and physiological factors that contribute to the aetiology of IBS remain poorly understood. Consequently, clinical management of IBS is reduced to symptom management through various suboptimal options. Recent evidence has suggested human milk oligosaccharides (HMOs) as a potential therapeutic option for IBS. Here, we review literature concerning the role of HMOs in IBS, including data from intervention and in vitro trials. HMO supplementation shows promising results in altering the gut microbiota and improving IBS symptoms, for instance by stimulating bifidobacteria. Further research in adults is required into HMO mechanisms, to confirm the preliminary results available to date and recommendations of HMO use in IBS.

Qualitative and quantitative mass spectrometry comparison of characteristic galactosyl lactose isomers from goat milk at different lactation stages

Galactooligosaccharides are composed mainly of galactosyl lactose, which is important for infant growth and as a functional food additive. Although galactosyl lactose is abundant in goat milk, its complex structure has hindered the separation and analysis of its isomers. In this study, 5 isomers of goat milk galactosyl lactose were separated by HPLC: β6'-galactosyl lactose (β6'-GL), α6'-galactosyl lactose (α6'-GL), β4'-galactosyl lactose (β4'-GL), α3'-galactosyl lactose (α3'-GL), and β3'-galactosyl lactose (β3'-GL). This composition differs from that of commercial galactooligosaccharide products, which comprise mainly β-configuration oligosaccharides. The isomers were then qualitatively and quantitatively compared at different lactation stages using online HPLC-mass spectrometry. Relative quantitative analysis showed that the total content of the 5 galactosyl lactose isomers was highest in transitional goat milk. Specifically, β3'-GL was the main isomer in colostrum and α3'-GL was the main isomer in transitional and mature milk. β6'-Galactosyl lactose and β4'-GL tended to increase and then decrease during lactation. Moreover, α3'-GL content was 2 times higher than in colostrum and 10 times higher in transitional milk than in mature milk; in contrast, for β3'-GL, the values were 5 and 2 times higher, respectively. Absolute quantitative analysis revealed that β3'-GL was the most abundant isomers in colostrum (32.3 mg/L), and α3'-GL was the most abundant in transitional milk (88.1 mg/L) and mature milk (36.3 mg/L). These findings provide an important quantitative basis for understanding the relationship between structure and function of galactosyl lactose in goat milk, as well as its exploitation as a functional food.

Infant formulas with synthetic oligosaccharides and respective marketing practices

Human milk contains more than 150 different oligosaccharides, which together are among to the quantitatively predominant solid components of breast milk. The oligosaccharide content and composition of human milk show large inter-individual differences. Oligosaccharide content is mostly influenced by genetic variants of the mother's secretor status. Oligosaccharides in human milk are utilized by infants' intestinal bacteria, affecting bacterial composition and metabolic activity. Maternal secretor status, and respective differing fucosylated oligosaccharide content, has been associated both with reduced and increased risk of infection in different populations of breastfed infants, possibly due to environmental conditions and the infant's genotype. There are no safety concerns regarding the addition of previously approved oligosaccharides to infant formula; however, no firm conclusions can be drawn about clinically relevant benefits either. Therefore, infant formulas with synthetic oligosaccharide additives are currently not preferentially recommended over infant formulas without such additives. We consider the use of terms such as "human milk oligosaccharides" and corresponding abbreviations such as "HMO" in any advertising of infant formula to be an inappropriate idealization of infant formula. Manufacturers should stop this practice, and such marketing practices should be prevented by responsible supervisory authorities. Pediatricians should inform families that infant formulas supplemented with synthetic oligosaccharides do not resemble the complex oligosaccharide composition of human milk.

Treponema primitia α1-2-fucosyltransferase-catalyzed one-pot multienzyme synthesis of fucosylated oligosaccharide lacto-N-fucopentaose I with antiviral activity against enterovirus 71

Fucosylated oligosaccharides have important biological functions as well as an excellent antiviral activity. A novel α 1-2-fucosyltransferase (α 2FT) from Treponema primitia (Tp2FT) was cloned and expressed in Escherichia coli BL21(DE3) and purified as an N-His6-tagged fusion protein (His6-Tp2FT). Mass spectrometry was carried out to identify the products of enzymatic reaction. The Tp2FT exhibited strict acceptor substrate specificity for type 1 structure (Galβ1-3GlcNAc)-containing glycans. It might be a promising emzyme for the chemo-enzymatic synthesis of lacto-N-fucopentaose I (LNFP I), which is one of the important fucosylated oligosaccharides. In this study, different in vitro experiments were used to study the biological activities of LNFP I. It could reduce the concentrations of inflammatory cytokines and effectively inhibit the synthesis of enterovirus 71 proliferation. LNFP I was an inhibitor of enterovirus 71 in the early stages of infection, it can used in infant nutrition and might provide a new drug for hand foot mouth disease.

Combining galacto-oligosaccharides and 2'-fucosyllactose alters their fermentation kinetics by infant fecal microbiota and influences AhR-receptor dependent cytokine responses in immature dendritic cells

Galacto-oligosaccharides (GOS) and 2′-fucosyllactose (2′-FL) are non-digestible carbohydrates (NDCs) that are often added to infant formula to replace the functionalities of human milk oligosaccharides (HMOs). It is not known if combining GOS and 2′-FL will affect their fermentation kinetics and subsequent immune-modulatory effects such as AhR-receptor stimulation. Here, we used an in vitro set-up for the fermentation of 2′-FL and GOS, either individually or combined, by fecal microbiota of 8-week-old infants. We found that GOS was fermented two times faster by the infant fecal microbiota when combined with 2′-FL, while the combination of GOS and 2′-FL did not result in a complete degradation of 2′-FL. Fermentation of both GOS and 2′-FL increased the relative abundance of Bifidobacterium, which coincided with the production of acetate and lactate. Digesta of the fermentations influenced dendritic cell cytokine secretion differently under normal conditions and in the presence of the AhR-receptor blocker CH223191. We show that, combining GOS and 2′-FL accelerates GOS fermentation by the infant fecal microbiota of 8-week-old infants. In addition, we show that the fermentation digesta of GOS and 2′-FL, either fermented individually or combined, can attenuate DC cytokine responses in a similar and in an AhR-receptor dependent way.

Galacto-oligosaccharides (GOS) and 2′-fucosyllactose (2′-FL) are non-digestible carbohydrates (NDCs) that are often added to infant formula to replace the functionalities of human milk oligosaccharides (HMOs).

Glycosyltransferase from Bacteroides gallinaceum Is a Novel α-1,3-Fucosyltransferase that Can Be Used for 3-Fucosyllactose Production In Vivo by Metabolically Engineered Escherichia coli

As one of the attractive fucosylated human milk oligosaccharides, the biological production of 3-fucosyllactose (3-FL) has received great attention, as it exhibits many excellent physiological functions for infants. In this work, a novel 3-FL-producing α-1,3-fucosyltransferase (α1,3-FucT) named FutM2 from Bacteroides gallinaceum was first selected from nine potential candidates in the NCBI database. Then, a highly 3-FL-producing engineered Escherichia coli strain was constructed by modular pathway enhancement including the GDL-l-fucose precursor supply by overexpressing manC, manB, gmd, and wcaG (CBGW), and the 3-FL synthesis pathway by introducing B. gallinaceum FutM2. Finally, a titer of 20.3 g L^-1 and productivity of 0.40 g L^-1 h^-1 of 3-FL were achieved in the 3-L bioreactor by engineered E. coli (ΔlacZΔwcaJ) harboring pCDF-CBGW and pET-futM2. Our study provided a novel α1,3-FucT from B. gallinaceum that could be used for 3-FL production, presenting an efficient microbial cell factory platform to de novo synthesize 3-FL from glycerol.

Intestinal Dysbiosis in the Infant and the Future of Lacto-Engineering to Shape the Developing Intestinal Microbiome

PURPOSE

The goal of this study was to review the role of human milk in shaping the infant intestinal microbiota and the potential of human milk bioactive molecules to reverse trends of increasing intestinal dysbiosis and dysbiosis-associated diseases.

METHODS

This narrative review was based on recent and historic literature.

FINDINGS

Human milk immunoglobulins, oligosaccharides, lactoferrin, lysozyme, milk fat globule membranes, and bile salt-stimulating lipase are complex multifunctional bioactive molecules that, among other important functions, shape the composition of the infant intestinal microbiota.

IMPLICATIONS

The co-evolution of human milk components and human milk-consuming commensal anaerobes many thousands of years ago resulted in a stable low-diversity infant microbiota. Over the past century, the introduction of antibiotics and modern hygiene practices plus changes in the care of newborns have led to significant alterations in the intestinal microbiota, with associated increases in risk of dysbiosis-associated disease. A better understanding of mechanisms by which human milk shapes the intestinal microbiota of the infant during a vulnerable period of development of the immune system is needed to alter the current trajectory and decrease intestinal dysbiosis and associated diseases.

Distinct fermentation of human milk oligosaccharides 3-FL and LNT2 and GOS/inulin by infant gut microbiota and impact on adhesion of Lactobacillus plantarum WCFS1 to gut epithelial cells

Human milk oligosaccharides (hMOs) are unique bioactive components in human milk. 3-Fucosyllactose (3-FL) is an abundantly present hMO that can be produced in sufficient amounts to allow application in infant formula. Lacto-N-triaose II (LNT2) can be obtained by acid hydrolysis of lacto-N-neotetraose (LNnT). Both 3-FL and LNT2 have been shown to have health benefits, but their impact on infant microbiota composition and microbial metabolic products such as short-chain fatty acids (SCFAs) is unknown. To gain more insight in fermentability, we performed in vitro fermentation studies of 3-FL and LNT2 using pooled fecal microbiota from 12-week-old infants. The commonly investigated galacto-oligosaccharides (GOS)/inulin (9 : 1) served as control. Compared to GOS/inulin, we observed a delayed utilization of 3-FL, which was utilized at 60.3% after 36 h of fermentation, and induced the gradual production of acetic acid and lactic acid. 3-FL specifically enriched bacteria of Bacteroides and Enterococcus genus. LNT2 was fermented much faster. After 14 h of fermentation, 90.1% was already utilized, and production of acetic acid, succinic acid, lactic acid and butyric acid was observed. LNT2 specifically increased the abundance of Collinsella, as well as Bifidobacterium. The GOS present in the GOS/inulin mixture was completely fermented after 14 h, while for inulin, only low DP was rapidly utilized after 14 h. To determine whether the fermentation might lead to enhanced colonization of commensal bacteria to gut epithelial cells, we investigated adhesion of the commensal Lactobacillus plantarum WCFS1 to Caco-2 cells. The fermentation digesta of LNT2 collected after 14 h, 24 h, and 36 h, and GOS/inulin after 24 h of fermentation significantly increased the adhesion of L. plantarum WCFS1 to Caco-2 cells, while 3-FL had no such effect. Our findings illustrate that fermentation of hMOs is very structure-dependent and different from the commonly applied GOS/inulin, which might lead to differential potencies to stimulate adhesion of commensal cells to gut epithelium and consequent microbial colonization. This knowledge might contribute to the design of tailored infant formulas containing specific hMO molecules to meet the need of infants during the transition from breastfeeding to formula.

Efficient Production of 2'-Fucosyllactose from l-Fucose via Self-Assembling Multienzyme Complexes in Engineered Escherichia coli

2'-Fucosyllactose (2'-FL) has been widely used as a nutritional additive in infant formula due to its multifarious nutraceutical and pharmaceutical functions in neonate health. As such, it is essential to develop an efficient and extensive microbial fermentation platform to cater to the needs of the 2'-FL market. In this study, a spatial synthetic biology strategy was employed to promote 2'-FL biosynthesis in recombinant Escherichia coli. First, the salvage pathway for 2'-FL production from l-fucose and lactose was constructed by introducing a bifunctional enzyme l-fucokinase/GDP-l-fucose pyrophosphorylase (Fkp) derived from Bacteroides fragilis and an α-1,2-fucosyltransferase (FutC) derived from Helicobacter pylori into engineered E. coli BL21(DE3). Next, the endogenous genes involved in the degradation and shunting of the substrate and key intermediate were inactivated to improve the availability of precursors for 2'-FL biosynthesis. Moreover, to further improve the yield and titer of 2'-FL, a short peptide pair (RIAD-RIDD) was used to form self-assembling multienzyme complexes in vivo. The spatial localization of peptides and stoichiometry of enzyme assemblies were subsequently optimized to further improve 2'-FL production. Finally, cofactor regeneration was also considered to alleviate the potential cofactor deficiency and redox flux imbalance in the biocatalysis process. Fed-batch fermentation of the final WLS20 strain accumulated 30.5 g/L extracellular 2'-FL with the yield and productivity of 0.661 mol/mol fucose and 0.48 g/L/h, respectively. This research has demonstrated that the application of spatial synthetic biology and metabolic engineering strategies can dramatically enlarge the titer and yield of 2'-FL biosynthesis in engineered E. coli.

Chicory inulin enhances fermentation of 2'-fucosyllactose by infant fecal microbiota and differentially influences immature dendritic cell and T-cell cytokine responses under normal and Th2-polarizing conditions

Scope: Non-digestible carbohydrates (NDCs) such as native chicory inulin and 2'-fucosyllactose (2'-FL) are added to infant formula to mimic some of the human milk oligosaccharide (HMO) functions. It is unknown whether combining inulin and 2'-FL influences their fermentation kinetics and whether the immune-modulatory effects of these NDCs are different under normal and inflammatory-prone Th2-polarizing conditions. Methods and results: We investigated the in vitro fermentation of 2'-FL and native chicory inulin, fermented individually and combined, using fecal inocula of 8-week-old infants. Native inulin was fermented in a size-dependent fashion and expedited the fermentation of 2'-FL. Fermentation of both native inulin and 2'FL increased the relative abundance of Bifidobacterium, which coincided with the production of acetate and lactate. The fermentation digesta of all fermentations differentially influenced both dendritic cell and T-cell cytokine responses under normal culture conditions or in presence of the Th2-polarizing cytokines IL-33 and TSLP, with the most pronounced effect for IL-1β in the presence of TSLP. Conclusions: Our findings show that native inulin can expedite the fermentation of 2'-FL by infant fecal microbiota and that these NDC fermentation digesta have different effects under normal and Th2-polarizing conditions, indicating that infants with different immune backgrounds might benefit from tailored NDC formulations.

Human Milk Oligosaccharides: A Comprehensive Review towards Metabolomics

Human milk oligosaccharides (HMOs) are the third most represented component in breast milk. They serve not only as prebiotics but they exert a protective role against some significant neonatal pathologies such as necrotizing enterocolitis. Furthermore, they can program the immune system and consequently reduce allergies and autoimmune diseases’ incidence. HMOs also play a crucial role in brain development and in the gut barrier’s maturation. Moreover, the maternal genetic factors influencing different HMO patterns and their modulation by the interaction and the competition between active enzymes have been widely investigated in the literature, but there are few studies concerning the role of other factors such as maternal health, nutrition, and environmental influence. In this context, metabolomics, one of the newest “omics” sciences that provides a snapshot of the metabolites present in bio-fluids, such as breast milk, could be useful to investigate the HMO content in human milk. The authors performed a review, from 2012 to the beginning of 2021, concerning the application of metabolomics to investigate the HMOs, by using Pubmed, Researchgate and Scopus as source databases. Through this technology, it is possible to know in real-time whether a mother produces a specific oligosaccharide, keeping into consideration that there are other modifiable and unmodifiable factors that influence HMO production from a qualitative and a quantitative point of view. Although further studies are needed to provide clinical substantiation, in the future, thanks to metabolomics, this could be possible by using a dipstick and adding the eventual missing oligosaccharide to the breast milk or formula in order to give the best and the most personalized nutritional regimen for each newborn, adjusting to different necessities.

Glycan Assembly Strategy: From Concept to Application

Glycans have been hot topics in recent years due to their exhibition of numerous biological activities. However, the heterogeneity of their natural source and the complexity of their chemical synthesis impede the progress in their biological research. Thus, the development of glycan assembly strategies to acquire plenty of structurally well-defined glycans is an important issue in carbohydrate chemistry. In this review, the latest advances in glycan assembly strategies from concepts to their applications in carbohydrate synthesis, including chemical and enzymatic/chemo-enzymatic approaches, as well as solution-phase and solid-phase/tag-assisted synthesis, are summarized. Furthermore, the automated glycan assembly techniques are also outlined.

Synthesis as an Expanding Resource in Human Milk Science

Few classes of natural products rival the structural audacity of oligosaccharides. Their complexity, however, has stood as an immense roadblock to translational research, as access to homogeneous material from nature is challenging. Thus, while carbohydrates are critical to the myriad functional and structural aspects of the biological sciences, their behavior is largely descriptive. This challenge presents an attractive opportunity for synthetic chemistry, particularly in the area of human milk science. First, there is an inordinate need for synthesizing homogeneous human milk oligosaccharides (HMOs). Superimposed on this goal is the mission of conducting syntheses at scale to enable animal studies. Herein, we present a personalized rumination of our involvement, and that of our colleagues, which has led to the synthesis and characterization of HMOs and mechanistic probes. Along the way, we highlight chemical, chemoenzymatic, and synthetic biology based approaches. We close with a discussion on emergent challenges and opportunities for synthesis, broadly defined, in human milk science.

Physiological effects, biosynthesis, and derivatization of key human milk tetrasaccharides, lacto-N-tetraose, and lacto-N-neotetraose

Human milk oligosaccharides (HMOs) have recently attracted ever-increasing interest because of their versatile physiological functions. In HMOs, two tetrasaccharides, lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT), constitute the essential components, each accounting 6% (w/w) of total HMOs. Also, they serve as core structures for fucosylation and sialylation, generating functional derivatives and elongation generating longer chains of core structures. LNT, LNnT, and their fucosylated and/or sialylated derivatives account for more than 30% (w/w) of total HMOs. For derivatization, LNT and LNnT can be modified into a series of complex fucosylated and/or sialylated HMOs by transferring fucose residues at α1,2-, α1,3-, and α1,3/4-linkage and/or sialic acid residues at α2,3- and α2,6-linkage. Such structural diversity allows these HMOs to possess great commercial value and an application potential in the food and pharmaceutical industries. In this review, we first elaborate the physiological functions of these tetrasaccharides and derivatives. Next, we extensively review recent developments in the biosynthesis of LNT, LNnT, and their derivatives in vitro and in vivo by employing advanced enzymatic reaction systems and metabolic engineering strategies. Finally, future perspectives in the synthesis of these HMOs using enzymatic and metabolic engineering approaches are presented.

Human milk oligosaccharides and non-digestible carbohydrates prevent adhesion of specific pathogens via modulating glycosylation or inflammatory genes in intestinal epithelial cells

Human milk oligosaccharides (hMOs) and non-digestible carbohydrates (NDCs) are known to inhibit the adhesion of pathogens to the gut epithelium, but the mechanisms involved are not well understood. Here, the effects of 2'-FL, 3-FL, DP3-DP10, DP10-DP60 and DP30-DP60 inulins and DM7, DM55 and DM69 pectins were studied on pathogen adhesion to Caco-2 cells. As the growth phase influences virulence, E. coli ET8, E. coli LMG5862, E. coli O119, E. coli WA321, and S. enterica subsp. enterica LMG07233 from both log and stationary phases were tested. Specificity for enteric pathogens was tested by including the lung pathogen K. pneumoniae LMG20218. Expression of the cell membrane glycosylation genes of galectin and glycocalyx and inflammatory genes was studied in the presence and absence of 2'-FL or NDCs. Inhibition of pathogen adhesion was observed for 2'-FL, inulins, and pectins. Pre-incubation with 2'-FL downregulated ICAM1, and pectins modified the glycosylation genes. In contrast, K. pneumoniae LMG20218 downregulated the inflammatory genes, but these were restored by pre-incubation with pectins, which reduced the adhesion of K. pneumoniae LMG20218. In addition, DM69 pectin significantly upregulated the inflammatory genes. 2'-FL and pectins but not inulins inhibited pathogen adhesion to the gut epithelial Caco-2 cells through changing the cell membrane glycosylation and inflammatory genes, but the effects were molecule-, pathogen-, and growth phase-dependent.

Engineering analysis of multienzyme cascade reactions for 3'-sialyllactose synthesis

Sialo‐oligosaccharides are important products of emerging biotechnology for complex carbohydrates as nutritional ingredients. Cascade bio‐catalysis is central to the development of sialo‐oligosaccharide production systems, based on isolated enzymes or whole cells. Multienzyme transformations have been established for sialo‐oligosaccharide synthesis from expedient substrates, but systematic engineering analysis for the optimization of such transformations is lacking. Here, we show a mathematical modeling‐guided approach to 3ʹ‐sialyllactose (3SL) synthesis from N‐acetyl‐ d‐neuraminic acid (Neu5Ac) and lactose in the presence of cytidine 5ʹ‐triphosphate, via the reactions of cytidine 5ʹ‐monophosphate‐Neu5Ac synthetase and α2,3‐sialyltransferase. The Neu5Ac was synthesized in situ from N‐acetyl‐ d‐mannosamine using the reversible reaction with pyruvate by Neu5Ac lyase or the effectively irreversible reaction with phosphoenolpyruvate by Neu5Ac synthase. We show through comprehensive time‐course study by experiment and modeling that, due to kinetic rather than thermodynamic advantages of the synthase reaction, the 3SL yield was increased (up to 75%; 10.4 g/L) and the initial productivity doubled (15 g/L/h), compared with synthesis based on the lyase reaction. We further show model‐based optimization to minimize the total loading of protein (saving: up to 43%) while maintaining a suitable ratio of the individual enzyme activities to achieve 3SL target yield (61%–75%; 7–10 g/L) and overall productivity (3–5 g/L/h). Collectively, our results reveal the principal factors of enzyme cascade efficiency for 3SL synthesis and highlight the important role of engineering analysis to make multienzyme‐catalyzed transformations fit for oligosaccharide production.

Digestion, fermentation, and pathogen anti-adhesive properties of the hMO-mimic di-fucosyl-β-cyclodextrin

Human milk is widely acknowledged as the best food for infants, and that is not just because of nutritional features. Human milk also contains a plethora of bioactive molecules, including a large set of human milk oligosaccharides (hMOs). Especially fucosylated hMOs have received attention for their anti-adhesive effects on pathogens, preventing attachment to the intestine and infection. Because hMOs are generally challenging to produce in sufficient quantities to study and ultimately apply in (medical) infant formula, novel compounds that are inspired by hMO structures (so-called "mimics") are interesting compounds to produce and evaluate for their biological effects. Here we present our thorough study into the digestion, fermentation and anti-adhesive capacity of the novel compound di-fucosyl-β-cyclodextrin (DFβCD), which was inspired by the molecular structures of hMOs. We establish that DFβCD is not digested by α-amylase and also resistant to fermentation by microbial enzymes from a 9 month-old infant inoculum. In addition, we reveal that DFβCD blocks adhesion of enterotoxigenic E. coli (ETEC) to Caco-2 cells, especially when DFβCD is pre-incubated with ETEC prior to addition to the Caco-2 cells. This suggests that DFβCD functions through a decoy effect. We expect that our results inspire the generation and biological evaluation of other fucosylated hMOs and mimics, to obtain a comprehensive overview of the anti-adhesive power of fucosylated glycans.

Efficient Production of 3′-Sialyllactose by Single Whole-Cell in One-Pot Biosynthesis

Sialyllactose (SL) is one of the most important acidic oligosaccharides in human milk, which plays an important role in the health of infants. In this work, an efficient multi-enzyme cascade was developed in a single whole cell to produce 3′-SL. We constructed two compatible plasmids with double cloning sites to co-express four genes. Different combinations were assessed to verify the optimal catalytic ability. Then, the conversion temperature, pH, and stability under the optimal temperature and pH were investigated. Moreover, the optimal conversion conditions and surfactant concentration were determined. By using the optimal conditions (35 °C, pH 7.0, 20 mM polyphosphate, 10 mM cytidine monophosphate (CMP), 20 mM MgCl2), 25 mL and 4 L conversion systems were carried out to produce 3′-SL. Similar results were obtained between different volume conversion reactions, which led the maximum production of 3′-SL to reach 53 mM from 54.2 mM of sialic acid (SA) in the 25 mL system and 52.8 mM of 3′-SL from 53.8 mM of SA in the 4 L system. These encouraging results demonstrate that the developed single whole-cell multi-enzyme system exhibits great potential and economic competitiveness for the manufacture of 3′-SL.

Engineered Microbial Routes for Human Milk Oligosaccharides Synthesis

Human milk oligosaccharides (HMOs) are one of the important ingredients in human milk, which have attracted great interest due to their beneficial effect on the health of newborns. The large-scale production of HMOs has been researched using engineered microbial routes due to the availability, safety, and low cost of host strains. In addition, the development of molecular biology technology and metabolic engineering has promoted the effectiveness of HMOs production. According to current reports, 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), 3'-sialyllactose (3'-SL), 6'-sialyllactose (6'-SL), and some fucosylated HMOs with complex structures have been produced via the engineered microbial route, with 2'-FL having been produced the most. However, due to the uncertainty of metabolic patterns, the selection of host strains has certain limitations. Aside from that, the expression of appropriate glycosyltransferase in microbes is key to the synthesis of different HMOs. Therefore, finding a safe and efficient glycosyltransferase has to be addressed when using engineered microbial pathways. In this review, the latest research on the production of HMOs using engineered microbial routes is reported. The selection of host strains and adapting different metabolic pathways helped researchers designing engineered microbial routes that are more conducive to HMOs production.

Impact of dietary fibers in infant formulas on gut microbiota and the intestinal immune barrier

Human milk (HM) is the gold standard for the nutrition of infants. An important component of HM is human milk oligosaccharides (hMOs), which play an important role in gut microbiota colonization and gut immune barrier establishment, and thereby contribute to the maturation of the immune system in early life. Guiding these processes is important as disturbances have life-long health effects and can lead to the development of allergic diseases. Unfortunately, not all infants can be exclusively fed with HM. These infants are routinely fed with infant formulas that contain hMO analogs and other non-digestible carbohydrates (NDCs) to mimic the effects of hMOs. Currently, the hMO analogs 2'-fucosyllactose (2'-FL), galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), and pectins are added to infant formulas; however, these NDCs cannot mimic all hMO functions and therefore new NDCs and NDC mixtures need to become available for specific groups of neonates like preterm and disease-prone neonates. In this review, we discuss human data on the beneficial effects of infant formula supplements such as the specific hMO analog 2'-FL and NDCs as well as their mechanism of effects like stimulation of microbiota development, maturation of different parts of the gut immune barrier and anti-pathogenic effects. Insights into the structure-specific mechanisms by which hMOs and NDCs exert their beneficial functions might contribute to the development of new tailored NDCs and NDC mixtures. We also describe the needs for new in vitro systems that can be used for research on hMOs and NDCs. The current data suggest that "tailored infant formulas" for infants of different ages and healthy statuses are needed to ensure a healthy development of the microbiota and the gut immune system of infants.

Membrane separation processes for enrichment of bovine and caprine milk oligosaccharides from dairy byproducts

Breast milk is an ideal source of human milk oligosaccharides (HMOs) for isolation and purification. However, breast milk is not for sale and at most is distributed to neonatal intensive care units as donor milk. To overcome this limitation, isolating HMOs analogs including bovine milk oligosaccharides (BMOs) and caprine milk oligosaccharides (CMOs) from other sources is timely and significant. Advances in the development of equipment and analytical methods have revealed that dairy processing byproducts are good sources of BMOs and CMOs. Enrichment of these oligosaccharides from dairy byproducts, such as whey, permeate, and mother liquor, is of increasing academic and economic value. The commonly employed approach for oligosaccharides purification is chromatographic technique, but it is only used at lab scale. In the dairy industry, chromatographic methods (large-scale ion exchange, 10,000 L size) are currently routinely used for the isolation/purification of milk proteins (e.g., lactoferrin). In contrast, membrane technology has been proven to be a suitable approach for the isolation and purification of BMOs and CMOs from dairy byproducts. Therefore, this review simply introduces BMOs and CMOs in dairy processing byproducts. This review also summarizes membrane separation processes for isolating and purifying BMOs and CMOs from different dairy byproducts. Finally, the technological challenges and solutions of each processing strategy are discussed in detail.

Enhanced bioproduction of fucosylated oligosaccharide 3-fucosyllactose in engineered Escherichia coli with an improved de novo pathway

3-fucosyllactose (3-FL) and 2'-fucosyllactose (2'-FL), are two important fucosylated oligosaccharides in human milk. Extensive studies on 2'-FL enabled its official approval for use in infant formula. However, development of 3-FL has been somewhat sluggish due to its low content in human milk and poor yield in enlarged production. Here, an α-1,3-fucosyltransferase mutant was introduced into an engineered Escherichia coli (E. coli) capable of producing GDP-L-fucose, leading to a promising 3-FL titer in a 5.0-L bioreactor. To increase the availability of cofactors (NADPH and GTP) for optimized 3-FL production, zwf, pntAB, and gsk genes were successively overexpressed, finally resulting in a higher 3-FL level with a titer of 35.72 g/L and a yield of 0.82 mol 3-FL/mol lactose. Unexpectedly, the deletion of pfkA gene led to a much lower performance of 3-FL production than the control strain. Still, our strategy achieved the highest 3-FL level in E. coli to date.

Human Milk Microbiota and Oligosaccharides: A Glimpse into Benefits, Diversity, and Correlations

Human milk represents a cornerstone for growth and development of infants, with extensive array of benefits. In addition to exceptionally nutritive and bioactive components, human milk encompasses a complex community of signature bacteria that helps establish infant gut microbiota, contributes to maturation of infant immune system, and competitively interferes with pathogens. Among bioactive constituents of milk, human milk oligosaccharides (HMOs) are particularly significant. These are non-digestible carbohydrates forming the third largest solid component in human milk. Valuable effects of HMOs include shaping intestinal microbiota, imparting antimicrobial effects, developing intestinal barrier, and modulating immune response. Moreover, recent investigations suggest correlations between HMOs and milk microbiota, with complex links possibly existing with environmental factors, genetics, geographical location, and other factors. In this review, and from a physiological and health implications perspective, milk benefits for newborns and mothers are highlighted. From a microbiological perspective, a focused insight into milk microbiota, including origins, diversity, benefits, and effect of maternal diet is presented. From a metabolic perspective, biochemical, physiological, and genetic significance of HMOs, and their probable relations to milk microbiota, are addressed. Ongoing research into mechanistic processes through which the rich biological assets of milk promote development, shaping of microbiota, and immunity is tackled.

Breast Milk: A Source of Functional Compounds with Potential Application in Nutrition and Therapy

Breast milk is an unbeatable food that covers all the nutritional requirements of an infant in its different stages of growth up to six months after birth. In addition, breastfeeding benefits both maternal and child health. Increasing knowledge has been acquired regarding the composition of breast milk. Epidemiological studies and epigenetics allow us to understand the possible lifelong effects of breastfeeding. In this review we have compiled some of the components with clear functional activity that are present in human milk and the processes through which they promote infant development and maturation as well as modulate immunity. Milk fat globule membrane, proteins, oligosaccharides, growth factors, milk exosomes, or microorganisms are functional components to use in infant formulas, any other food products, nutritional supplements, nutraceuticals, or even for the development of new clinical therapies. The clinical evaluation of these compounds and their commercial exploitation are limited by the difficulty of isolating and producing them on an adequate scale. In this work we focus on the compounds produced using milk components from other species such as bovine, transgenic cattle capable of expressing components of human breast milk or microbial culture engineering.

Biotechnological Production of 2'-Fucosyllactose: A Prevalent Fucosylated Human Milk Oligosaccharide

Human milk oligosaccharide (HMO) is a key component of human milk carbohydrates and is closely related to the nutrition and health benefits of breastfeeding in infants. 2'-Fucosyllactose (2'-FL) is the most abundant fucosylated HMO, which has remarkable value in nutrition and medicine, such as suppressing pathogen infection, regulating intestinal flora, and boosting immunity. However, 2'-FL production via the method of extraction or chemical synthesis cannot meet its large demand, and as a result, environmentally friendly and efficient biotechnological approaches, including in vitro enzymatic synthesis and microbial cell factory production, have been developed and applied to its commercialized production. This review introduces, summarizes, and discusses the recent advances in the biotechnological production of 2'-FL. Furthermore, future research directions for the biotechnological production of 2'-FL as well as the strategies to further improve its concentration are highlighted and discussed.

Recent approaches for the quantitative analysis of functional oligosaccharides used in the food industry: A review

Functional oligosaccharides (OS) are diverse groups of carbohydrates that confer several health benefits stemming from their prebiotic activity. Commonly used oligosaccharides, fructooligosaccharides and galactooligosaccharides, are used in a wide range of applications from food ingredients to mimic the prebiotic activity of human milk oligosaccharides (HMOs) in infant formula to sugar and fat replacers in dairy and bakery products. However, while consumption of these compounds is associated with several positive health effects, increased consumption can cause intestinal discomfort and aggravation of intestinal bowel syndrome symptoms. Hence, it is essential to develop rapid and reliable techniques to quantify OS for quality control and proper assessment of their functionality in food and food products. The present review will focus on recent analytical techniques used to quantify OS in different matrices such as food and beverage products.

Unlocking Nature's Biosynthetic Power-Metabolic Engineering for the Fermentative Production of Chemicals

Fermentation as a production method for chemicals is especially attractive, as it is based on cheap renewable raw materials and often exhibits advantages in terms of costs and sustainability. The tremendous development of technology in bioscience has resulted in an exponentially increasing knowledge about biological systems and has become the main driver for innovations in the field of metabolic engineering. Progress in recombinant DNA technology, genomics, and computational methods open new, cheaper, and faster ways to metabolically engineer microorganisms. Existing biosynthetic pathways for natural products, such as vitamins, organic acids, amino acids, or secondary metabolites, can be discovered and optimized efficiently, thereby enabling competitive commercial production processes. Novel biosynthetic routes can now be designed by the rearrangement of nature's unlimited number of enzymes and metabolic pathways in microbial strains. This expands the range of chemicals accessible by biotechnology and has yielded the first commercial products, while new fermentation technologies targeting novel active ingredients, commodity chemicals, and CO₂ -fixation methods are on the horizon.

Biological strategies for oligo/polysaccharide synthesis: biocatalyst and microbial cell factory

Oligosaccharides and polysaccharides constitute the principal components of carbohydrates, which are important biomacromolecules that demonstrate considerable bioactivities. However, the variety and structural complexity of oligo/polysaccharides represent a major challenge for biological and structural explorations. To access structurally defined oligo/polysaccharides, biological strategies using glycoenzyme biocatalysts have shown remarkable synthetic potential attributed to their regioselectivity and stereoselectivity that allow mild, structurally controlled reaction without addition of protecting groups necessary in chemical strategies. This review summarizes recent biotechnological approaches of oligo/polysaccharide synthesis, which mainly includes in vitro enzymatic synthesis and cell factory synthesis. We have discussed the important factors involved in the production of nucleotide sugars. Furthermore, the strategies established in the cell factory and enzymatic syntheses are summarized, and we have highlighted concepts like metabolic flux rebuilding and regulation, enzyme engineering, and route design as important strategies. The research challenges and prospects are also outlined and discussed.

Multi-Path Optimization for Efficient Production of 2'-Fucosyllactose in an Engineered Escherichia coli C41 (DE3) Derivative

2′-fucosyllactose (2′-FL), one of the simplest but most abundant oligosaccharides in human milk, has been demonstrated to have many positive benefits for the healthy development of newborns. However, the high-cost production and limited availability restrict its widespread use in infant nutrition and further research on its potential functions. In this study, on the basis of previous achievements, we developed a powerful cell factory by using a lacZ-mutant Escherichia coli C41 (DE3)ΔZ to ulteriorly increase 2′-FL production by feeding inexpensive glycerol. Initially, we co-expressed the genes for GDP-L-fucose biosynthesis and heterologous α-1,2-fucosyltransferase in C41(DE3)ΔZ through different plasmid-based expression combinations, functionally constructing a preferred route for 2′-FL biosynthesis. To further boost the carbon flux from GDP-L-fucose toward 2′-FL synthesis, deletion of chromosomal genes (wcaJ, nudD, and nudK) involved in the degradation of the precursors GDP-L-fucose and GDP-mannose were performed. Notably, the co-introduction of two heterologous positive regulators, RcsA and RcsB, was confirmed to be more conducive to GDP-L-fucose formation and thus 2′-FL production. Further a genomic integration of an individual copy of α-1,2-fucosyltransferase gene, as well as the preliminary optimization of fermentation conditions enabled the resulting engineered strain to achieve a high titer and yield. By collectively taking into account the intracellular lactose utilization, GDP-L-fucose availability, and fucosylation activity for 2′-FL production, ultimately a highest titer of 2′-FL in our optimized conditions reached 6.86 g/L with a yield of 0.92 mol/mol from lactose in the batch fermentation. Moreover, the feasibility of mass production was demonstrated in a 50-L fed-batch fermentation system in which a maximum titer of 66.80 g/L 2′-FL was achieved with a yield of 0.89 mol 2′-FL/mol lactose and a productivity of approximately 0.95 g/L/h 2′-FL. As a proof of concept, our preliminary 2′-FL production demonstrated a superior production performance, which will provide a promising candidate process for further industrial production.