Bioengineered 2′-fucosyllactose and 3-fucosyllactose inhibit the adhesion of Pseudomonas aeruginosa and enteric pathogens to human intestinal and respiratory cell lines

Human milk oligosaccharides: bridging the gap in intestinal microbiota between mothers and infants

Breast milk is an essential source of infant nutrition. It is also a vital determinant of the structure and function of the infant intestinal microbial community, and it connects the mother and infant intestinal microbiota. Human milk oligosaccharides (HMOs) are a critical component in breast milk. HMOs can reach the baby's colon entirely from milk and become a fermentable substrate for some intestinal microorganisms. HMOs can enhance intestinal mucosal barrier function and affect the intestinal function of the host through immune function, which has a therapeutic effect on specific infant intestinal diseases, such as necrotizing enterocolitis. In addition, changes in infant intestinal microbiota can reflect the maternal intestinal microbiota. HMOs are a link between the maternal intestinal microbiota and infant intestinal microbiota. HMOs affect the intestinal microbiota of infants and are related to the maternal milk microbiota. Through breastfeeding, maternal microbiota and HMOs jointly affect infant intestinal bacteria. Therefore, HMOs positively influence the establishment and balance of the infant microbial community, which is vital to ensure infant intestinal function. Therefore, HMOs can be used as a supplement and alternative therapy for infant intestinal diseases.

Natural anti-adhesive components against pathogenic bacterial adhesion and infection in gastrointestinal tract: case studies of Helicobacter pylori, Salmonella enterica, Clostridium difficile, and diarrheagenic Escherichia coli

Antimicrobial resistance (AMR) poses a global public health concern. Recognizing the critical role of bacterial adhesion in pathogenesis of infection, anti-adhesive therapy emerges as a promising approach to impede initial bacterial attachment, thus preventing pathogenic colonization and infection. Natural anti-adhesive agents derived from food sources are generally safe and have the potential to inhibit the emergence of resistant bacteria. This comprehensive review explored diverse natural dietary components exhibiting anti-adhesive activities against several model enteric pathogens, including Helicobacter pylori, Salmonella enterica, Clostridium difficile, and three key diarrheagenic Escherichia coli (i.e., enterotoxigenic E. coli, enteropathogenic E. coli, and enterohemorrhagic E. coli). Investigating various anti-adhesive products will advance our understanding of current research of the field and inspire further development of these agents as potential nutraceuticals or adjuvants to improve the efficacy of conventional antibiotics.

The Association Between Maternal Psychological Health and Human Milk Oligosaccharide Composition

Background and Objective: Human milk oligosaccharides (HMOs) are carbohydrates abundant in human breast milk. Their composition varies widely among women, and prior research has identified numerous factors contributing to this variation. However, the relationship between maternal psychological health and HMO levels is currently unknown. Thus, our objective was to identify whether maternal stress, anxiety, or depressive symptoms are associated with HMOs. Methods: Data originated from 926 lactating individuals from the UC San Diego Human Milk Biorepository. Nineteen prevalent HMOs were assayed using high-performance liquid chromatography. Participants self-reported measures of the Edinburgh Postnatal Depression Scale (n = 495), State-Trait Anxiety Inventory S-Scale (n = 486), and/or Perceived Stress Scale (n = 493) within 60 days of their milk collection; their results were categorized using standard screening cutoffs. HMOs were assessed individually and grouped by principal component analysis (PCA), and associations with maternal psychological symptoms were analyzed using multivariable linear regression adjusted for covariates. Results: After Bonferroni correction (p < 0.002), the following HMOs significantly varied with maternal psychological distress in multivariate analysis: lacto-N-fucopentaose III (LNFP III) and lacto-N-hexaose (LNH) among Secretors with depressive symptoms and difucosyllactose (DFLac), LNFP III, and disialyl-LNH (DSLNH) among Secretors with stress. In PCA, depressive symptoms and stress were associated with one principal component among Secretors. No HMOs varied with anxiety symptoms. Conclusions: Several HMOs varied with maternal depressive symptoms and stress, suggesting a relationship between maternal psychological health and breast milk composition. Additional studies are needed to determine the impact of this variation on infant health.

Human Milk Oligosaccharides and Their Pivotal Role in Gut-Brain Axis Modulation and Neurologic Development: A Narrative Review to Decipher the Multifaceted Interplay

BACKGROUND

Human milk oligosaccharides (HMOs), which are unique bioactive components in human milk, are increasingly recognized for their multifaceted roles in infant health. A deeper understanding of the nexus between HMOs and the gut-brain axis can revolutionize neonatal nutrition and neurodevelopmental strategies.

METHODS

We performed a narrative review using PubMed, Embase, and Google Scholar to source relevant articles. The focus was on studies detailing the influence of HMOs on the gut and brain systems, especially in neonates. Articles were subsequently synthesized based on their exploration into the effects and mechanisms of HMOs on these interconnected systems.

RESULTS

HMOs significantly influence the neonatal gut-brain axis. Specific concentrations of HMO, measured 1 and 6 months after birth, would seem to agree with this hypothesis. HMOs are shown to influence gut microbiota composition and enhance neurotransmitter production, which are crucial for brain development. For instance, 2'-fucosyllactose has been demonstrated to support cognitive development by fostering beneficial gut bacteria that produce essential short-chain fatty acids.

CONCLUSIONS

HMOs serve as crucial modulators of the neonatal gut-brain axis, underscoring their importance in infant nutrition and neurodevelopment. Their dual role in shaping the infant gut while influencing brain function presents them as potential game-changers in neonatal health strategies.

Recent advances of 3-fucosyllactose in health effects and production

Human milk oligosaccharides (HMOs) have been recognized as gold standard for infant development. 3-Fucosyllactose (3-FL), being one of the Generally Recognized as Safe HMOs, represents a core trisaccharide within the realm of HMOs; however, it has received comparatively less attention in contrast to extensively studied 2'-fucosyllactose. The objective of this review is to comprehensively summarize the health effects of 3-FL, including its impact on gut microbiota proliferation, antimicrobial effects, immune regulation, antiviral protection, and brain maturation. Additionally, the discussion also covers the commercial application and regulatory approval status of 3-FL. Lastly, an organized presentation of large-scale production methods for 3-FL aims to provide a comprehensive guide that highlights current strategies and challenges in optimization.

Combinatorial Optimization Strategies for 3-Fucosyllactose Hyperproduction in Escherichia coli

3-Fucosyllactose (3-FL), an important fucosylated human milk oligosaccharide in breast milk, offers numerous health benefits to infants. Previously, we metabolically engineered Escherichia coli BL21(DE3) for the in vivo biosynthesis of 3-FL. In this study, we initially optimized culture conditions to double 3-FL production. Competing pathway genes involved in in vivo guanosine 5'-diphosphate-fucose biosynthesis were subsequently inactivated to redirect fluxes toward 3-FL biosynthesis. Next, three promising transporters were evaluated using plasmid-based or chromosomally integrated expression to maximize extracellular 3-FL production. Additionally, through analysis of α1,3-fucosyltransferase (FutM2) structure, we identified Q126 residues as a highly mutable residue in the active site. After site-saturation mutation, the best-performing mutant, FutM2-Q126A, was obtained. Structural analysis and molecular dynamics simulations revealed that small residue replacement positively influenced helical structure generation. Finally, the best strain BD3-A produced 6.91 and 52.1 g/L of 3-FL in a shake-flask and fed-batch cultivations, respectively, highlighting its potential for large-scale industrial applications.

Combinatorial Engineering of Escherichia coli for Enhancing 3-Fucosyllactose Production

3-Fucosyllactose (3-FL) is an important fucosylated human milk oligosaccharide (HMO) with biological functions such as promoting immunity and brain development. Therefore, the construction of microbial cell factories is a promising approach to synthesizing 3-FL from renewable feedstocks. In this study, a combinatorial engineering strategy was used to achieve efficient de novo 3-FL production in Escherichia coli. α-1,3-Fucosyltransferase (futM2) from Bacteroides gallinaceum was introduced into E. coli and optimized to create a 3-FL-producing chassis strain. Subsequently, the 3-FL titer increased to 5.2 g/L by improving the utilization of the precursor lactose and down-regulating the endogenous competitive pathways. Furthermore, a synthetic membraneless organelle system based on intrinsically disordered proteins was designed to spatially regulate the pathway enzymes, producing 7.3 g/L 3-FL. The supply of the cofactors NADPH and GTP was also enhanced, after which the 3-FL titer of engineered strain E26 was improved to 8.2 g/L in a shake flask and 10.8 g/L in a 3 L fermenter. In this study, we developed a valuable approach for constructing an efficient 3-FL-producing cell factory and provided a versatile workflow for other chassis cells and HMOs.

Residents or Tourists: Is the Lactating Mammary Gland Colonized by Residential Microbiota?

The existence of the human milk microbiome has been widely recognized for almost two decades, with many studies examining its composition and relationship to maternal and infant health. However, the richness and viability of the human milk microbiota is surprisingly low. Given that the lactating mammary gland houses a warm and nutrient-rich environment and is in contact with the external environment, it may be expected that the lactating mammary gland would contain a high biomass microbiome. This discrepancy raises the question of whether the bacteria in milk come from true microbial colonization in the mammary gland ("residents") or are merely the result of constant influx from other bacterial sources ("tourists"). By drawing together data from animal, in vitro, and human studies, this review will examine the question of whether the lactating mammary gland is colonized by a residential microbiome.

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.

Pre-clinical safety assessment of biotechnologically produced lacto-N-tetraose (LNT)

Lacto-N-tetraose (LNT) is a human milk oligosaccharide with average concentrations ranging from 0.74 to 1.07 g/L in breastmilk, depending on the lactation stage. In this study, the preclinical safety of LNT produced by the Escherichia coli K-12 E2083 production strain was assessed. LNT was negative in both the bacterial reverse mutation assay and the in vitro micronucleus assay, demonstrating the absence of genotoxic potential for this substance. In the OECD 408 guideline compliant 90-day oral toxicity study rat, LNT did not induce any adverse effects in any treatment group up to and including the highest dose tested, and no LOAEL could be determined. Therefore, the no-observed-adverse effect level (NOAEL) is set at the highest dose level tested, i.e. a dietary level of 5 % (w/w), corresponding to ≥2856 mg/kg bw/day and ≥3253 mg/kg bw/day for males and females, respectively. This might be an underestimation of the NOAEL, caused by the range of dose levels tested. The results obtained in the current study are in good agreement with available data generated using other biotechnologically produced LNT batches and therefore support its safe use as a food ingredient.

Rational Design of an α-1,3-Fucosyltransferase for the Biosynthesis of 3-Fucosyllactose in Bacillus subtilis ATCC 6051a via De Novo GDP-l-Fucose Pathway

3-Fucosyllactose (3-FL) is an important oligosaccharide and nutrient in breast milk that can be synthesized in microbial cells by α-1,3-fucosyltransferase (α-1,3-FucT) using guanosine 5'-diphosphate (GDP)-l-fucose and lactose as substrates. However, the catalytic efficiency of known α-1,3-FucTs from various sources was limited due to their low solubility. To enhance the microbial production of 3-FL, the efficiencies of α-1,3-FucTs were evaluated and in Bacillus subtilis (B. subtilis) chassis cells that had been endowed with a heterologous synthetic pathway for GDP-l-fucose, revealing that the activity of FucTa from Helicobacter pylori (H. pylori) was higher than that of any of other reported homologues. To further improve the catalytic performance of FucTa, a rational design approach was employed, involving intracellular evaluation of the mutational sites of M32 obtained through directed evolution, analysis of the ligand binding site diversity, and protein structure simulation. Among the obtained variants, the FucTa-Y218 K variant exhibited the highest 3-FL yield, reaching 7.55 g/L in the shake flask growth experiment, which was 3.48-fold higher than that achieved by the wild-type enzyme. Subsequent fermentation optimization in a 5 L bioreactor resulted in a remarkable 3-FL production of 36.98 g/L, highlighting the great prospects of the designed enzyme and the strains for industrial applications.

Structural and binding studies of 2'- and 3-fucosyllactose and its complexes with norovirus capsid protein by molecular dynamics simulations

Human breast milk contains free oligosaccharides (Human Milk Oligosaccharides-HMOs) that help to protect breastfed infants against a variety of infectious diseases and act as decoy receptors. In breast milk, HMOs are the third most abundant compounds after lactose and lipids. Structural and conformational models of HMOs are quite crucial to studying the interaction with proteins and molecular recognition phenomenon. Molecular dynamics simulations for two trisaccharides HMOs (2'-FL and 3-FL) were carried out for 250 ns and the conformational models were subsequently substantiated by three replicate simulations. The conformer models of HMOs 2'-FL and 3-FL were deposited in the 3-Dimensional Structural Database for Sialic acid-containing CARbohydrates (3DSDSCAR) database website (www.3dsdscar.in). HMOs were then docked into the active site of norovirus capsid protein and are simulated for 100 ns duration. Each complex system was stabilized by direct and water-mediated hydrogen bonding interactions. Binding free energy calculations predict two possible binding modes for each complex system. The conformational flexibility and binding stability of the complex systems were calculated. The protein folding/unfolding and compactness seem to be better for the two HMOs. From a general perspective, we found that both 2'-FL and 3-FL exhibited higher binding efficacy towards norovirus capsid protein and according to the structural stability, 3-FL might be used as a preventive inhibitor for norovirus infection.Communicated by Ramaswamy H. Sarma.

Determinants of microbial colonization in the premature gut

Abnormal microbial colonization in the gut at an early stage of life affects growth, development, and health, resulting in short- and long-term adverse effects. Microbial colonization patterns of preterm infants differ from those of full-term infants in that preterm babies and their mothers have more complicated prenatal and postnatal medical conditions. Maternal complications, antibiotic exposure, delivery mode, feeding type, and the use of probiotics may significantly shape the gut microbiota of preterm infants at an early stage of life; however, these influences subside with age. Although some factors and processes are difficult to intervene in or avoid, understanding the potential factors and determinants will help in developing timely strategies for a healthy gut microbiota in preterm infants. This review discusses potential determinants of gut microbial colonization in preterm infants and their underlying mechanisms.

Infants Fed Breastmilk or 2'-FL Supplemented Formula Have Similar Systemic Levels of Microbiota-Derived Secondary Bile Acids

Human milk represents an optimal source of nutrition during infancy. Milk also serves as a vehicle for the transfer of growth factors, commensal microbes, and prebiotic compounds to the immature gastrointestinal tract. These immunomodulatory and prebiotic functions of milk are increasingly appreciated as critical factors in the development of the infant gut and its associated microbial community. Advances in infant formula composition have sought to recapitulate some of the prebiotic and immunomodulatory functions of milk through human milk oligosaccharide (HMO) fortification, with the aim of promoting healthy development both within the gastrointestinal tract and systemically. Our objective was to investigate the effects of feeding formulas supplemented with the HMO 2'-fucosyllactose (2'-FL) on serum metabolite levels relative to breastfed infants. A prospective, randomized, double-blinded, controlled study of infant formulas (64.3 kcal/dL) fortified with varying levels of 2'-FL and galactooligosaccharides (GOS) was conducted [0.2 g/L 2'-FL + 2.2 g/L GOS; 1.0 g/L 2'-FL + 1.4 g/L GOS]. Healthy singleton infants age 0-5 days and with birth weight > 2490 g were enrolled (n = 201). Mothers chose to either exclusively formula-feed or breastfeed their infant from birth to 4 months of age. Blood samples were drawn from a subset of infants at 6 weeks of age (n = 35-40 per group). Plasma was evaluated by global metabolic profiling and compared to a breastfed reference group (HM) and a control formula (2.4 g/L GOS). Fortification of control infant formula with the HMO 2'-FL resulted in significant increases in serum metabolites derived from microbial activity in the gastrointestinal tract. Most notably, secondary bile acid production was broadly increased in a dose-dependent manner among infants receiving 2'-FL supplemented formula relative to the control formula. 2'-FL supplementation increased secondary bile acid production to levels associated with breastfeeding. Our data indicate that supplementation of infant formula with 2'-FL supports the production of secondary microbial metabolites at levels comparable to breastfed infants. Thus, dietary supplementation of HMO may have broad implications for the function of the gut microbiome in systemic metabolism. This trial was registered at with the U.S. National library of Medicine as NCT01808105.

Infant Fecal Fermentations with Galacto-Oligosaccharides and 2′-Fucosyllactose Show Differential Bifidobacterium longum Stimulation at Subspecies Level

The objective of the current study was to evaluate the potential of 2′-FL and GOS, individually and combined, in beneficially modulating the microbial composition of infant and toddler (12–18 months) feces using the micro-Matrix bioreactor. In addition, the impacts of GOS and 2′-FL, individually and combined, on the outgrowth of fecal bifidobacteria at (sub)species level was investigated using the baby M-SHIME® model. For young toddlers, significant increases in the genera Bifidobacterium, Veillonella, and Streptococcus, and decreases in Enterobacteriaceae, Clostridium XIVa, and Roseburia were observed in all supplemented fermentations. In addition, GOS, and combinations of GOS and 2′-FL, increased Collinsella and decreased Salmonella, whereas 2′-FL, and combined GOS and 2′-FL, decreased Dorea. Alpha diversity increased significantly in infants with GOS and/or 2′-FL, as well as the relative abundances of the genera Veillonella and Akkermansia with 2′-FL, and Lactobacillus with GOS. Combinations of GOS and 2′-FL significantly stimulated Veillonella, Lactobacillus, Bifidobacterium, and Streptococcus. In all supplemented fermentations, Proteobacteria decreased, with the most profound decreases accomplished by the combination of GOS and 2′-FL. When zooming in on the different (sub)species of Bifidobacterium, GOS and 2’-FL were shown to be complementary in stimulating breast-fed infant-associated subspecies of Bifidobacterium longum in a dose-dependent manner: GOS stimulated Bifidobacterium longum subsp. longum, whereas 2′-FL supported outgrowth of Bifidobacterium longum subsp. infantis.

Engineering Pheromone-Mediated Quorum Sensing with Enhanced Response Output Increases Fucosyllactose Production in Saccharomyces cerevisiae

Engineering dynamic control of gene expression is desirable because many engineered functions interfere with endogenous cellular processes that have evolved to facilitate growth and survival. Minimizing conflict between growth and production phases can therefore improve product titers in microbial cell factories. We developed an autoinduced gene expression system by rewiring the Saccharomyces cerevisiae pheromone response pathway. To ameliorate growth reduction due to the early onset response at low population densities, α-pheromone of Kluyveromyces lactis (Kα) instead of S. cerevisiae (Sα) was expressed in mating type "a" yeast. Kα-induced expression of pathway genes was further enhanced by the transcriptional activator Gal4p expressed under the control of the pheromone-responsive FUS1 promoter (P_fus1). As a demonstration, the engineered circuit combined with the deletion of the endogenous galactose metabolic pathway genes was applied to the production of human milk oligosaccharides, 2'-fucosyllactose (2'-FL) and 3-fucosllactose (3-FL). The engineered strains produced 3.37 g/L 2'-FL and 2.36 g/L 3-FL on glucose with a volumetric productivity of 0.14 and 0.03 g/L·h^-1 in batch flask cultivation, respectively. These represented 147 and 153% increases over the control strains on galactose wherein the respective pathway genes are expressed under GAL promoters only. Further fed-batch fermentation achieved titers of 32.05 and 20.91 g/L for 2' and 3-FL, respectively. The genetic program developed here thus represents a promising option for implementing dynamic regulation in yeast and could be used for the production of biochemicals that may place a heavy metabolic burden on cell growth.

Human Milk Oligosaccharides as Potential Antibiofilm Agents: A Review

Surface-associated bacterial communities called biofilms are ubiquitous in nature. Biofilms are detrimental in medical settings due to their high tolerance to antibiotics and may alter the final pathophysiological outcome of many healthcare-related infections. Several innovative prophylactic and therapeutic strategies targeting specific mechanisms and/or pathways have been discovered and exploited in the clinic. One such emerging and original approach to dealing with biofilms is the use of human milk oligosaccharides (HMOs), which are the third most abundant solid component in human milk after lactose and lipids. HMOs are safe to consume (GRAS status) and act as prebiotics by inducing the growth and colonization of gut microbiota, in addition to strengthening the intestinal epithelial barrier, thereby protecting from pathogens. Moreover, HMOs can disrupt biofilm formation and inhibit the growth of specific microbes. In the present review, we summarize the potential of HMOs as antibacterial and antibiofilm agents and, hence, propose further investigations on using HMOs for new-age therapeutic interventions.

The analysis of 2'-fucosyllactose concentration in Korean maternal milk using LC-MS/MS

Despite health benefits reported recently, 2'-fucosyllactose (2'-FL) concentration in maternal milk was not conclusively reported because it varies between countries and mothers. Particularly, its distribution among Korean mothers was not obtained from a reliable sample group yet. Thus, a dynamic range for 2'-FL concentration in Korean mothers' milk was investigated from 102 samples. A quantitative method using multiple reaction monitoring (MRM) by triple-quadrupole-mass spectrometry has been evaluated by a standard procedure of method validation. The 2'-FL concentration was in the range of 0.4 to 2.6 g/L overall. While the samples from secretor mothers (n = 80) contained 1.0 to 2.8 g/L of 2'-FL, the maternal milk from non-secretor mothers (n = 22) had 0.01 to 0.06 g/L of 2'-FL only. In addition to the genetic variation of mothers, the lactation period impacted the 2'-FL concentration. The average 2'-FL concentration of the late-stage group (> 60 days) was 78% of that obtained from the first month of postpartum mothers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01154-4.

Human Milk Oligosaccharide 2'-Fucosyllactose Inhibits Ligand Binding to C-Type Lectin DC-SIGN but Not to Langerin

Human milk oligosaccharides (HMOs) and their most abundant component, 2'-Fucosyllactose (2'-FL), are known to be immunomodulatory. Previously, it was shown that HMOs and 2'-FL bind to the C-type lectin receptor DC-SIGN. Here we show, using a ligand-receptor competition assay, that a whole mixture of HMOs from pooled human milk (HMOS) and 2'-FL inhibit the binding of the carbohydrate-binding receptor DC-SIGN to its prototypical ligands, fucose and the oligosaccharide Lewis-B, (Le^b) in a dose-dependent way. Interestingly, such inhibition by HMOS and 2'-FL was not detected for another C-type lectin, langerin, which is evolutionarily similar to DC-SIGN. The cell-ligand competition assay using DC-SIGN expressing cells confirmed that 2'-FL inhibits the binding of DC-SIGN to Le^b. Molecular dynamic (MD) simulations show that 2'-FL exists in a preorganized bioactive conformation before binding to DC-SIGN and this conformation is retained after binding to DC-SIGN. Le^b has more flexible conformations and utilizes two binding modes, which operate one at a time via its two fucoses to bind to DC-SIGN. Our hypothesis is that 2'-FL may have a reduced entropic penalty due to its preorganized state, compared to Le^b, and it has a lower binding enthalpy, suggesting a better binding to DC-SIGN. Thus, due to the better binding to DC-SIGN, 2'-FL may replace Le^b from its binding pocket in DC-SIGN. The MD simulations also showed that 2'-FL does not bind to langerin. Our studies confirm 2'-FL as a specific ligand for DC-SIGN and suggest that 2'-FL can replace other DC-SIGN ligands from its binding pocket during the ligand-receptor interactions in possible immunomodulatory processes.

Module-Guided Metabolic Rewiring for Fucosyllactose Biosynthesis in Engineered Escherichia coli with Lactose De Novo Pathway

Fucosyllactose (FL) has garnered considerable attention for its benefits on infant health. In this study, we report an efficient E. coli cell factory to produce 2'/3-fucosyllactose (2'/3-FL) with lactose de novo pathway through metabolic network remodeling, including (1) modification of the PTS^Glc system to enhance glucose internalization efficiency; (2) screening for β-1,4-galactosyltransferase (β-1,4-GalT) and introduction of lactose synthesis pathway; (3) eliminating inhibition of byproduct pathways; (4) constructing antibiotic-free and inducer-free FL strains; and (5) up-regulating the expression of genes in the GDP-l-fucose module. The final engineered strains BP10-3 and BP11-3 produced 4.36 g/L for 2'-FL and 3.23 g/L for 3-FL in shake flasks. In 3 L bioreactors, fed-batch cultivations of the two strains produced 40.44 g/L for 2'-FL and 30.42 g/L for 3-FL, yielding 0.63 and 0.69 g/g glucose, respectively. The strategy described in this work will help to engineer E. coli as a safe chassis for other lactose-independent HMOs production.

Effects of addition of 2-fucosyllactose to infant formula on growth and specific pathways of utilization by Bifidobacterium in healthy term infants

Oligosaccharides in human milk support health via intestinal microbiome. We studied effects of addition of 2-fucosyllactose (2′FL) to the infant formula on infant growth, occurrence of adverse events (AE), and infant microbiome, including expression of microbial genes that metabolize 2′FL. Our hypothesis was that while 2′FL would not affect growth, it would cause changes in microbiome metabolism. In a double-blinded randomized controlled study fashion, the infant formula ± 2′FL or human milk was fed to healthy term infants for 16 weeks. Fecal samples obtained at baseline and week 16 were analyzed for microbial populations, metagenomic species concept (MGS), and genetics of gut metabolic modules (GMMs). There were no effects of addition of 2′FL on growth or AEs. There were no significant differences by feeding group in MGS richness or Shannon diversity at baseline, but formula groups each had significantly greater richness (p < 0.05) and diversity (p < 0.05) after 16 weeks of feeding than the breastfed group. While two glycosyl hydrolase (GH) families (GH42 and GH112) were significantly increased, two other GH families (GH20 and GH2) were significantly decreased in the test formula group compared to the control formula group; although modest, addition of 2′FL resulted in changes in microbiome in the direction of breastfed infants, consistent with internal metabolism of HMOs by Bifidobacterium.

Exploring the Potential of Human Milk and Formula Milk on Infants’ Gut and Health

Early-life gut microbiota plays a role in determining the health and risk of developing diseases in later life. Various perinatal factors have been shown to contribute to the development and establishment of infant gut microbiota. One of the important factors influencing the infant gut microbial colonization and composition is the mode of infant feeding. While infant formula milk has been designed to resemble human milk as much as possible, the gut microbiome of infants who receive formula milk differs from that of infants who are fed human milk. A diverse microbial population in human milk and the microbes seed the infant gut microbiome. Human milk contains nutritional components that promote infant growth and bioactive components, such as human milk oligosaccharides, lactoferrin, and immunoglobulins, which contribute to immunological development. In an attempt to encourage the formation of a healthy gut microbiome comparable to that of a breastfed infant, manufacturers often supplement infant formula with prebiotics or probiotics, which are known to have a bifidogenic effect and can modulate the immune system. This review aims to elucidate the roles of human milk and formula milk on infants’ gut and health.

Growth and Gastrointestinal Tolerance in Healthy Term Infants Fed Milk-Based Infant Formula Supplemented with Five Human Milk Oligosaccharides (HMOs): A Randomized Multicenter Trial

Background: Five of the most abundant human milk oligosaccharides (HMOs) in human milk are 2′-fucosyllactose (2′-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), 3′-sialyllactose (3′-SL) and 6′-sialyllactose (6′-SL). Methods: A randomized, double-blind, controlled parallel feeding trial evaluated growth in healthy term infants fed a control milk-based formula (CF; n = 129), experimental milk-based formula (EF; n = 130) containing five HMOs (5.75 g/L; 2′-FL, 3-FL, LNT, 3′-SL and 6′-SL) or human milk (HM; n = 104). Results: No significant differences (all p ≥ 0.337, protocol evaluable cohort) were observed among the three groups for weight gain per day from 14 to 119 days (D) of age, irrespective of COVID-19 or combined non-COVID-19 and COVID-19 periods. There were no differences (p ≥ 0.05) among the three groups for gains in weight and length from D14 to D119. Compared to the CF group, the EF group had more stools that were soft, frequent and yellow and were similar to the HM group. Serious and non-serious adverse events were not different among groups, but more CF-fed infants were seen by health care professionals for illness from study entry to D56 (p = 0.044) and D84 (p = 0.028) compared to EF-fed infants. Conclusions: The study demonstrated that the EF containing five HMOs supported normal growth, gastrointestinal (GI) tolerance and safe use in healthy term infants.

Engineered Bacillus subtilis for the de novo production of 2'-fucosyllactose

BACKGROUND

The most abundant human milk oligosaccharide in breast milk, 2'-fucosyllactose (2'-FL), has been approved as an additive to infant formula due to its multifarious nutraceutical and pharmaceutical functions in promoting neonate health. However, the low efficiency of de novo synthesis limits the cost-efficient bioproduction of 2'-FL.

RESULTS

This study achieved 2'-FL de novo synthesis in a generally recognized as safe (GRAS) strain Bacillus subtilis. First, a de novo biosynthetic pathway for 2'-FL was introduced by expressing the manB, manC, gmd, wcaG, and futC genes from Escherichia coli and Helicobacter pylori in B. subtilis, resulting in 2'-FL production of 1.12 g/L. Subsequently, a 2'-FL titer of 2.57 g/L was obtained by reducing the competitive lactose consumption, increasing the regeneration of the cofactor guanosine-5'-triphosphate (GTP), and enhancing the supply of the precursor mannose-6-phosphate (M6P). By replacing the native promoter of endogenous manA gene (encoding M6P isomerase) with a constitutive promoter P7, the 2'-FL titer in shake flask reached 18.27 g/L. The finally engineered strain BS21 could produce 88.3 g/L 2'-FL with a yield of 0.61 g/g lactose in a 3-L bioreactor, without the addition of antibiotics and chemical inducers.

CONCLUSIONS

The efficient de novo synthesis of 2'-FL can be achieved by the engineered B. subtilis, paving the way for the large-scale bioproduction of 2'-FL titer in the future.

Prebiotics as a Tool for the Prevention and Treatment of Obesity and Diabetes: Classification and Ability to Modulate the Gut Microbiota

Diabetes and obesity are metabolic diseases that have become alarming conditions in recent decades. Their rate of increase is becoming a growing concern worldwide. Recent studies have established that the composition and dysfunction of the gut microbiota are associated with the development of diabetes. For this reason, strategies such as the use of prebiotics to improve intestinal microbial structure and function have become popular. Consumption of prebiotics for modulating the gut microbiota results in the production of microbial metabolites such as short-chain fatty acids that play essential roles in reducing blood glucose levels, mitigating insulin resistance, reducing inflammation, and promoting the secretion of glucagon-like peptide 1 in the host, and this accounts for the observed remission of metabolic diseases. Prebiotics can be either naturally extracted from non-digestible carbohydrate materials or synthetically produced. In this review, we discussed current findings on how the gut microbiota and microbial metabolites may influence host metabolism to promote health. We provided evidence from various studies that show the ability of prebiotic consumption to alter gut microbial profile, improve gut microbial metabolism and functions, and improve host physiology to alleviate diabetes and obesity. We conclude among other things that the application of systems biology coupled with bioinformatics could be essential in ascertaining the exact mechanisms behind the prebiotic–gut microbe–host interactions required for diabetes and obesity improvement.

Neonatal subchronic toxicity and in vitro genotoxicity studies of the human-identical milk oligosaccharide 3-fucosyllactose

Human milk oligosaccharides, such as 3-fucosyllactose (3-FL), are bioactive components of breast milk associated with benefits for infant growth and development. Structurally identical compounds (human-identical milk oligosaccharides - HiMOs) can be produced using microbial fermentation, allowing their use in infant formula to increase its similarity with human milk. Toxicological studies are required to demonstrate safety of HiMOs and that of any impurities potentially carried over from the manufacturing process. Biotechnologically produced 3-FL was tested for potential genotoxicity (bacterial reverse mutation test and in vitro mammalian micronucleus test) and subchronic toxicity (90-day study with neonatal rats). In the 90-day study, 3-FL was administered by gavage to rats once daily from Day 7 of age, at doses up to 4000 mg/kg body weight (bw)/day (the maximum feasible dose), followed by a 4-week recovery period. Reference controls received 4000 mg/kg bw/day of oligofructose, an ingredient permitted for use in infant formula. Results for the genotoxicity studies were negative. In the 90-day study, there were no adverse effects of 3-FL on any of the parameters measured; thus, the no-observed-adverse-effect level was 4000 mg/kg bw/day (the highest dose tested). These results support the safety of biotechnologically produced 3-FL for use in infant formula and other foods.

Occurrence, functional properties, and preparation of 3-fucosyllactose, one of the smallest human milk oligosaccharides

Human milk oligosaccharides (HMOs) are receiving wide interest and high attention due to their health benefits, especially for newborns. The HMOs-fortified products are expected to mimic human milk not only in the kinds of added oligosaccharides components but also the appropriate proportion between these components, and further provide the nutrition and physiological effects of human milk to newborns as closely as possible. In comparison to intensively studied 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL) has less attention in almost all respects. Nerveless, 3-FL naturally occurs in breast milk and increases roughly over the course of lactation with a nonnegligible content, and plays an irreplaceable role in human milk and delivers functional properties to newborns. According to the safety evaluation, 3-FL shows no acute oral toxicity, genetic toxicity, and subchronic toxicity. It has been approved as generally recognized as safe (GRAS). Biological production of 3-FL can be realized by enzymatic and cell factory approaches. The α1,3- or α1,3/4-fucosyltransferase is the key enzyme for 3-FL biosynthesis. Various metabolic engineering strategies have been applied to enhance 3-FL yield using cell factory approach. In conclusion, this review gives an overview of the recent scientific literatures regarding occurrence, bioactive properties, safety evaluation, and biotechnological preparation of 3-FL.

Effects of Different Feeding Methods on the Structure, Metabolism, and Gas Production of Infant and Toddler Intestinal Flora and Their Mechanisms

In this study, we evaluated the effects of different feeding methods on the characteristics of intestinal flora and gas production in infants and toddlers by using an in vitro simulated intestinal microecology fermentation and organoid model. We found that the feeding method influences intestinal gas and fecal ammonia production in infants and toddlers. Supplementation with milk powder for infants in the late lactation period could promote the proliferation of beneficial bacteria, including Bifidobacteria. Intestinal flora gas production in a culture medium supplemented with fucosyllactose (2′-FL) was significantly lower than that in media containing other carbon sources. In conclusion, 2′-FL may reduce gas production in infant and toddler guts through two mechanisms: first, it cannot be used by harmful intestinal bacteria to produce gas; second, it can inhibit intestinal mucosa colonization by harmful bacteria by regulating the expression of intestinal epithelial pathogenic genes/signaling pathways, thus reducing the proliferation of gas-producing harmful bacteria in the gut.

The prebiotic effect of human milk oligosaccharides 3'- and 6'-sialyllactose on adhesion and biofilm formation by Clostridioides difficile - pilot study

Bacterial adhesion is the first stage of colonisation and biofilm formation by Clostridioides difficile. Cell wall proteins (Cwp) 84 and 66 play crucial roles in the pathophysiology of C. difficile and may affect bacterial adhesion. Sialylated human milk oligosaccharides (HMOs) have potential to inhibit bacterial adhesion in vitro. The aim of this study was to investigate how 3'-sialyllactose (SL) and 6'-SL affect adhesion and C. difficile biofilm formation. Also, the influence of these substances on cwp84 and cwp66 genes expression by C. difficile was assessed. An adhesion assay was performed using three human colon cells in vitro, and biofilm formation was evaluated using crystal violet staining and confocal laser scanning microscopy. The effect of 3'-SL and 6'SL on cwp expression was measured using real time-PCR. Both tested HMOs decreased expression of the cwp84 gene, adhesion of C. difficile to human colon cells in vitro and biofilm formation.

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.

Enhancing biosynthesis of 2'-Fucosyllactose in Escherichia coli through engineering lactose operon for lactose transport and α -1,2-Fucosyltransferase for solubility

2'-Fucosyllactose (2'-FL) is the most abundant oligosaccharide in human milk and one of the most actively studied human milk oligosaccharides (HMO). When 2'-FL is produced through biological production using a microorganism, like Escherichia coli, D-lactose is often externally fed as an acceptor substrate for fucosyltransferase (FT). When D-glucose is used as a carbon source for the cell growth and D-lactose is transported by lactose permease (LacY) in lac operon, D-lactose transport is under the control of catabolite repression (CR), limiting the supply of D-lactose for FT reaction in the cell, hence decreasing the production of 2'-FL. In this study, a remarkable increase of 2'-FL production was achieved by relieving the CR from the lac operon of the host E. coli BL21 and introducing adequate site-specific mutations into α-1,2-FT (FutC) for enhancement of catalytic activity and solubility. For the host engineering, the native lac promoter (P_lac ) was substituted for tac promoter (P_tac ), so that the lac operon could be turned on, but not subjected to CR by high D-glucose concentration. Next, for protein engineering of FutC, family multiple sequence analysis for conserved amino acid sequences and protein-ligand substrate docking analysis led us to find several mutation sites, which could increase the solubility of FutC and its activity. As a result, a combination of four mutation sites (F40S/Q150H/C151R/Q239S) was identified as the best candidate, and the quadruple mutant of FutC enhanced 2'-FL titer by 2.4-fold. When the above-mentioned E. coli mutant host transformed with the quadruple mutant of futC was subjected to fed-batch culture, 40 g l^-1 of 2'-FL titer was achieved with the productivity of 0.55 g l^-1 h^-1 and the specific 2'-FL yield of 1.0 g g^-1 DCW. This article is protected by copyright. All rights reserved.

Human Milk Oligosaccharides Exhibit Biofilm Eradication Activity Against Matured Biofilms Formed by Different Pathogen Species

Human milk oligosaccharides (HMOs) have been shown to exhibit plenty of benefits for infants, such as prebiotic activity shaping the gut microbiota and immunomodulatory and anti-inflammatory activity. For some pathogenic bacteria, antimicrobial activity has been proved, but most studies focus on group B streptococci. In the present study, we investigated the antimicrobial and antibiofilm activities of the total and fractionated HMOs from pooled human milk against four common human pathogenic Gram-negative species (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Burkholderia cenocepacia) and three Gram-positive species (Staphylococcus aureus, Enterococcus faecium, and Enterococcus faecalis). The activity of HMOs against enterococci and B. cenocepacia are addressed here for the first time. We showed that HMOs exhibit a predominant activity against the Gram-positive species, with E. faecalis being the most sensitive to the HMOs, both in planktonic bacteria and in biofilms. In further tests, we could exclude fucosyllactose as the antibacterial component. The biological significance of these findings may lie in the prevention of skin infections of the mother’s breast as a consequence of breastfeeding-induced skin laceration and/or protection of the infants’ nasopharynx and lung from respiratory pathogens such as staphylococci.

Human Milk Oligosaccharides Reduce Murine Group B Streptococcus Vaginal Colonization with Minimal Impact on the Vaginal Microbiota

Group B Streptococcus (GBS) colonizes the vaginal mucosa of a significant percentage of healthy women and is a leading cause of neonatal bacterial infections. Currently, pregnant women are screened in the last month of pregnancy, and GBS-positive women are given antibiotics during parturition to prevent bacterial transmission to the neonate. Recently, human milk oligosaccharides (HMOs) isolated from breastmilk were found to inhibit GBS growth and biofilm formation in vitro, and women that make certain HMOs are less likely to be vaginally colonized with GBS. Using in vitro human vaginal epithelial cells and a murine vaginal colonization model, we tested the impact of HMO treatment on GBS burdens and the composition of the endogenous microbiota by 16S rRNA amplicon sequencing. HMO treatment reduced GBS vaginal burdens in vivo with minimal alterations to the vaginal microbiota. HMOs displayed potent inhibitory activity against GBS in vitro, but HMO pretreatment did not alter adherence of GBS or the probiotic Lactobacillus rhamnosus to human vaginal epithelial cells. In addition, disruption of a putative GBS glycosyltransferase (Δsan_0913) rendered the bacterium largely resistant to HMO inhibition in vitro and in vivo but did not compromise its adherence, colonization, or biofilm formation in the absence of HMOs. We conclude that HMOs are a promising therapeutic bioactive to limit GBS vaginal colonization with minimal impacts on the vaginal microenvironment.

IMPORTANCE During pregnancy, GBS ascension into the uterus can cause fetal infection or preterm birth. In addition, GBS exposure during labor creates a risk of serious disease in the vulnerable newborn and mother postpartum. Current recommended prophylaxis consists of administering broad-spectrum antibiotics to GBS-positive mothers during labor. Although antibiotics have significantly reduced GBS neonatal disease, there are several unintended consequences, including altered neonatal gut bacteria and increased risk for other types of infection. Innovative preventions displaying more targeted antimicrobial activity, while leaving the maternal microbiota intact, are thus appealing. Using a mouse model, we found that human milk oligosaccharides (HMOs) reduce GBS burdens without perturbing the vaginal microbiota. We conclude that HMOs are a promising alternative to antibiotics to reduce GBS neonatal disease.

Recent understanding of human milk oligosaccharides in establishing infant gut microbiome and roles in immune system

Human milk oligosaccharides (HMOs) are complex sugars with distinctive structural diversity present in breast milk. HMOs have various functional roles to play in infant development starting from establishing the gut microbiome and immune system to take it up to the mature phase. It has been a major energy source for human gut microbes that confer positive benefits on infant health by directly interacting through intestinal cells and generating short-chain fatty acids. It has recently become evident that each species of Bifidobacterium and other genera which are resident of the infant gut employ distinct molecular mechanisms to capture and digest diverse structural HMOs to avoid competition among themselves and successfully maintain gut homeostasis. HMOs also directly modulate gut immune responses and can decoy receptors of pathogenic bacteria and viruses, inhibiting their binding on intestinal cells, thus preventing the emergence of a disease. This review provides a critical understanding of how different gut bacteria capture and utilize selective sugars from the HMO pool and how different structural HMOs protect infants from infectious diseases.

Use of a Liquid Supplement Containing 2 Human Milk Oligosaccharides: The First Double-Blind, Randomized, Controlled Trial in Pre-term Infants

There is growing evidence supporting the benefit of human milk oligosaccharides (HMOs) on reducing risk of illnesses and improving immune function in newborn infants, but evidence in pre-term infants is lacking. This randomized, double-blind, placebo-controlled trial (NCT03607942) of pre-term infants evaluated the effects of HMO supplementation on feeding tolerance, growth, and safety in 7 neonatal units in France. Pre-term infants (27-33 weeks' gestation, birth weight <1,700 g) were randomized early after birth to receive HMO supplement (n = 43) [2'-fucosyllactose (2'FL) and lacto-N-neotetraose (LNnT) in a 10:1 ratio (0.374 g/kg body weight/day)] or an isocaloric placebo (n = 43) consisting of only glucose (0.140 g/kg/day) until discharge from the neonatal unit. Anthropometric z-scores were calculated using Fenton growth standards. Primary outcome was feeding tolerance, measured by non-inferiority (NI) in days to reach full enteral feeding (FEF) from birth in HMO vs. placebo group (NI margin = 4+ days). Mean number of days on intervention prior to FEF was 8.9 and 10.3 days in HMO and placebo, respectively. Non-inferiority in time to reach FEF in HMO (vs. placebo) was achieved [LS mean difference (95% CI) = -2.16 (-5.33, 1.00); upper bound of 95% CI < NI margin] in full analysis set and similar for per protocol. Adjusted mean time to reach FEF from birth was 2 days shorter in HMO (12.2) vs. placebo (14.3), although not statistically significant (p = 0.177). There was no difference in weight-for-age z-scores between groups throughout the FEF period until discharge. Length-for-age z-scores were higher in HMO at FEF day 14 [0.29 (0.02, 0.56), p = 0.037] and 21 [0.31 (0.02, 0.61), p = 0.037]. Head circumference-for-age z-score was higher in HMO vs. placebo at discharge [0.42 (0.12, 0.71), p = 0.007]. Occurrence of adverse events (AEs) was similar in both groups and relatively common in this population, whereas 2.3 and 14.3%, respectively, experienced investigator-confirmed, related AEs. HMO supplementation is safe and well-tolerated in pre-term infants. After 9 days of supplementation, the HMO group reached FEF 2 days earlier vs. placebo, although the difference was not statistically significant. In addition, HMO supplementation supports early postnatal growth, which may have a positive impact on long-term growth and developmental outcomes.

Metabolic engineering strategies of de novo pathway for enhancing 2'-fucosyllactose synthesis in Escherichia coli

2′‐Fucosyllactose (2′‐FL), one of the most abundant human milk oligosaccharides (HMOs), is used as a promising infant formula ingredient owing to its multiple health benefits for newborns. However, limited availability and high‐cost preparation have restricted its extensive use and intensive research on its potential functions. In this work, a powerful Escherichia coli cell factory was developed to ulteriorly increase 2′‐FL production. Initially, a modular pathway engineering was strengthened to balance the synthesis pathway through different plasmid combinations with a resulting maximum 2′‐FL titre of 1.45 g l⁻¹. To further facilitate the metabolic flux from GDP‐l‐fucose towards 2′‐FL, the CRISPR‐Cas9 system was utilized to inactivate the genes including lacZ and wcaJ, increasing the titre by 6.59‐fold. Notably, the co‐introduction of NADPH and GTP regeneration pathways was confirmed to be more conducive to 2′‐FL formation, achieving a 2′‐FL titre of 2.24 g l⁻¹. Moreover, comparisons of various exogenous α1,2‐fucosyltransferase candidates revealed that futC from Helicobacter pylori generated the highest titre of 2′‐FL. Finally, the viability of scaled‐up production of 2′‐FL was evidenced in a 3 l bioreactor with a maximum titre of 22.3 g l⁻¹ 2′‐FL and a yield of 0.53 mole 2′‐FL mole⁻¹ lactose.

Six Oligosaccharides' Variation in Breast Milk: A Study in South China from 0 to 400 Days Postpartum

This study investigated the variation in oligosaccharide levels in the breast milk of south Chinese mothers in a prolonged breastfeeding period of up to 400 days postpartum. A total of 488 breast milk samples were collected from 335 healthy mothers at five different time points: 0–5 days, 10–15 days, 40–45 days, 200–240 days, and 300–400 days postpartum. A high-performance anion-exchange chromatography-pulsed amperometric detector (HPAEC-PAD) was used to quantify 2′-fucosyllactose (2′-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), 3′-sialyllactose (3′-SL) and 6′-sialyllactose (6′-SL). In this study, we found six oligosaccharides that were present in breast milk from 0 to 400 days postpartum. The median value ranges of individual oligosaccharide components in this study were 1013–2891 mg/L 2′-FL, 193–1421 mg/L 3-FL, 314–1478 mg/L LNT, 44–255 mg/L LNnT, 111–241 mg/L 3′-SL, and 23–602 mg/L6′-SL. HMO levels decreased over the lactation periods, except for 3-FL, which increased throughout lactation. The predominant fucosylated and sialylated HMOs were 2′-FL and 6′-SL at 40–45 days postpartum and changed to 3-FL and 3′-SL at 200–240 days postpartum. Results from this study showed that lactating women continue to provide their offspring with a high level of 2′-FL one year after delivery, suggesting that 2′-FL may play an important role for infants in early life. Our findings also provide further evidence in support of breastfeeding after one-year postpartum.

Engineering Escherichia coli for highly efficient production of lacto-N-triose II from N-acetylglucosamine, the monomer of chitin

BACKGROUND

Lacto-N-triose II (LNT II), an important backbone for the synthesis of different human milk oligosaccharides, such as lacto-N-neotetraose and lacto-N-tetraose, has recently received significant attention. The production of LNT II from renewable carbon sources has attracted worldwide attention from the perspective of sustainable development and green environmental protection.

RESULTS

In this study, we first constructed an engineered E. coli cell factory for producing LNT II from N-acetylglucosamine (GlcNAc) feedstock, a monomer of chitin, by introducing heterologous β-1,3-acetylglucosaminyltransferase, resulting in a LNT II titer of 0.12 g L^-1. Then, lacZ (lactose hydrolysis) and nanE (GlcNAc-6-P epimerization to ManNAc-6-P) were inactivated to further strengthen the synthesis of LNT II, and the titer of LNT II was increased to 0.41 g L^-1. To increase the supply of UDP-GlcNAc, a precursor of LNT II, related pathway enzymes including GlcNAc-6-P deacetylase, glucosamine synthase, and UDP-N-acetylglucosamine pyrophosphorylase, were overexpressed in combination, optimized, and modulated. Finally, a maximum titer of 15.8 g L^-1 of LNT II was obtained in a 3-L bioreactor with optimal enzyme expression levels and β-lactose and GlcNAc feeding strategy.

CONCLUSIONS

Metabolic engineering of E. coli is an effective strategy for LNT II production from GlcNAc feedstock. The titer of LNT II could be significantly increased by modulating the gene expression strength and blocking the bypass pathway, providing a new utilization for GlcNAc to produce high value-added products.

Multifunctional Benefits of Prevalent HMOs: Implications for Infant Health

Breastfeeding is the best source of nutrition during infancy and is associated with a broad range of health benefits. However, there remains a significant and persistent need for innovations in infant formula that will allow infants to access a wider spectrum of benefits available to breastfed infants. The addition of human milk oligosaccharides (HMOs) to infant formulas represents the most significant innovation in infant nutrition in recent years. Although not a direct source of calories in milk, HMOs serve as potent prebiotics, versatile anti-infective agents, and key support for neurocognitive development. Continuing improvements in food science will facilitate production of a wide range of HMO structures in the years to come. In this review, we evaluate the relationship between HMO structure and functional benefits. We propose that infant formula fortification strategies should aim to recapitulate a broad range of benefits to support digestive health, immunity, and cognitive development associated with HMOs in breastmilk. We conclude that acetylated, fucosylated, and sialylated HMOs likely confer important health benefits through multiple complementary mechanisms of action.

Combining HPAEC-PAD, PGC-LC-MS, and 1D 1H NMR to Investigate Metabolic Fates of Human Milk Oligosaccharides in 1-Month-Old Infants: a Pilot Study

A solid-phase extraction procedure was optimized to extract 3-fucosyllactose and other human milk oligosaccharides (HMOs) from human milk samples separately, followed by absolute quantitation using high-performance anion-exchange chromatography-pulsed amperometric detection and porous graphitized carbon-liquid chromatography-mass spectrometry, respectively. The approach developed was applied on a pilot sample set of 20 human milk samples and paired infant feces collected at around 1 month postpartum. One-dimensional 1H nuclear magnetic resonance spectroscopy was employed on the same samples to determine the relative levels of fucosylated epitopes and sialylated (Neu5Ac) structural elements. Based on different HMO consumption patterns in the gastrointestinal tract, the infants were assigned to three clusters as follows: complete consumption; specific consumption of non-fucosylated HMOs; and, considerable levels of HMOs still present with consumption showing no specific preference. The consumption of HMOs by infant microbiota also showed structure specificity, with HMO core structures and Neu5Ac(α2-3)-decorated HMOs being most prone to degradation. The degree and position of fucosylation impacted HMO metabolization differently.

Regulation of hBD-2, hBD-3, hCAP18/LL37, and Proinflammatory Cytokine Secretion by Human Milk Oligosaccharides in an Organotypic Oral Mucosal Model

Human milk oligosaccharides (HMOs), the third largest solid fraction in human milk, can modulate inflammation through Toll-like receptor signaling, but little is known about their immunomodulatory potential in the oral cavity. In this study, we determined whether the HMOs 2′-fucosyllactose (2′-FL) and 3-fucosyllactose (3-FL) regulate human-beta defensin (hBD)-2 and -3, cathelicidin (hCAP18/LL-37), and cytokine responses in human gingival cells using a three-dimensional oral mucosal culture model. The model was incubated with 0.1% or 1% 2′-FL and 3-FL, alone and in combination, for 5 or 24 h, and hBD-2, hBD-3, and hCAP18/LL-37 were analyzed by immunohistochemistry. The expression profiles of interleukin (IL)-1, IL-1RA, IL-8, and monocyte chemoattractant protein (MCP)-1 were determined by LUMINEX immunoassay. The combination of 1% 2′-FL and 1% 3-FL, and 1% 3-FL alone, for 24 h upregulated hBD-2 protein expression significantly (p < 0.001 and p = 0.016, respectively). No changes in the other antimicrobial peptides or proinflammatory cytokines were observed. Thus, 3-FL, alone and in combination with 2′-FL, stimulates oral mucosal secretion of hBD-2, without effecting a proinflammatory response when studied in an oral mucosal culture model.

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.

Gold standard for nutrition: a review of human milk oligosaccharide and its effects on infant gut microbiota

Human milk is the gold standard for nutrition of infant growth, whose nutritional value is mainly attributed to human milk oligosaccharides (HMOs). HMOs, the third most abundant component of human milk after lactose and lipids, are complex sugars with unique structural diversity which are indigestible by the infant. Acting as prebiotics, multiple beneficial functions of HMO are believed to be exerted through interactions with the gut microbiota either directly or indirectly, such as supporting beneficial bacteria growth, anti-pathogenic effects, and modulation of intestinal epithelial cell response. Recent studies have highlighted that HMOs can boost infants health and reduce disease risk, revealing potential of HMOs in food additive and therapeutics. The present paper discusses recent research in respect to the impact of HMO on the infant gut microbiome, with emphasis on the molecular basis of mechanism underlying beneficial effects of HMOs.

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.

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.

The role of the blood group-related glycosyltransferases FUT2 and B4GALNT2 in susceptibility to infectious disease

The glycosylation profile of the gastrointestinal tract is an important factor mediating host-microbe interactions. Variation in these glycan structures is often mediated by blood group-related glycosyltransferases, and can lead to wide-ranging differences in susceptibility to both infectious- as well as chronic disease. In this review, we focus on the interplay between host glycosylation, the intestinal microbiota and susceptibility to gastrointestinal pathogens based on studies of two exemplary blood group-related glycosyltransferases that are conserved between mice and humans, namely FUT2 and B4GALNT2. We highlight that differences in susceptibility can arise due to both changes in direct interactions, such as bacterial adhesion, as well as indirect effects mediated by the intestinal microbiota. Although a large body of experimental work exists for direct interactions between host and pathogen, determining the more complex and variable mechanisms underlying three-way interactions involving the intestinal microbiota will be the subject of much-needed future research.