Cytokine induction by a linear 1,3-glucan, curdlan-oligo, in mouse leukocytes in vitro

Promoting substrates uptake and curdlan synthesis of Agrobacterium sp. by attenuating the exopolysaccharide encapsulation

During curdlan production by Agrobacterium sp., the secreted exopolysaccharide (EPS) gradually encapsulated Agrobacterium sp., accompanied by cell aggregation, resulted in inhibited substrate uptake and curdlan synthesis. To relieve the EPS encapsulation effect, the shake-flask culture medium was quantitatively supplemented with 2 % to 10 % endo-β-1,3-glucanase (BGN), while obtaining curdlan with a decreased weight-average molecular weight ranging from 18.99 × 10⁴ Da to 3.20 × 10⁴ Da. In a 7-L bioreactor, the 4 % BGN supplement substantially attenuated the EPS encapsulation, resulting in increased glucose consumption and curdlan yield to 66.41 g/L and 34.53 g/L after fermentation of 108 h, which improved 43 % and 67 %, respectively compared with the control. The disruption of EPS encapsulation with BGN treatment accelerated the regeneration of ATP and UTP, resulting in sufficient uridine diphosphate glucose for curdlan synthesis. The upregulation of related genes at the transcription level reveals that the respiratory metabolic intensity, the energy regeneration efficiency, and the curdlan synthetase activity were enhanced. This study presents a simple and novel strategy of relieving the effects of EPS encapsulation on the metabolism of Agrobacterium sp. for the high-yield and value-added production of curdlan, which could be potentially applied in producing other EPSs.

Functional and structural characterization of an endo-β-1,3-glucanase from Euglena gracilis

Endo-β-1,3-glucanases from several organisms have attracted much attention in recent years because of their capability for in vitro degrading β-1,3-glucan as a critical step for both biofuels production and short-chain oligosaccharides synthesis. In this study, we biochemically characterized a putative endo-β-1,3-glucanase (EgrGH64) belonging to the family GH64 from the single-cell protist Euglena gracilis. The gene coding for the enzyme was heterologously expressed in a prokaryotic expression system supplemented with 3% (v/v) ethanol to optimize the recombinant protein right folding. Thus, the produced enzyme was highly purified by immobilized-metal affinity and gel filtration chromatography. The enzymatic study demonstrated that EgrGH64 could hydrolyze laminarin (K_M 23.5 mg ml^-1,k_cat 1.20 s^-1) and also, but with less enzymatic efficiency, paramylon (K_M 20.2 mg ml^-1,k_cat 0.23 ml mg^-1 s^-1). The major product of the hydrolysis of both substrates was laminaripentaose. The enzyme could also use ramified β-glucan from the baker's yeast cell wall as a substrate (K_M 2.10 mg ml^-1, k_cat 0.88 ml mg^-1 s^-1). This latter result, combined with interfacial kinetic analysis evidenced a protein's greater efficiency for the yeast polysaccharide, and a higher number of hydrolysis sites in the β-1,3/β-1,6-glucan. Concurrently, the enzyme efficiently inhibited the fungal growth when used at 1.0 mg/mL (15.4 μM). This study contributes to assigning a correct function and determining the enzymatic specificity of EgrGH64, which emerges as a relevant biotechnological tool for processing β-glucans.

One-step production of functional branched oligoglucosides with coupled fermentation of Pichia pastoris GS115 and Sclerotium rolfsii WSH-G01

Endo-β-1,3-glucanase with high specific activity is a prerequisite for enzymatic preparation of valuable β-oligoglucosides. Heterologous expression in Pichia pastoris GS115 with error-prone PCR technology was implemented, and the mutant strain 7 N12 was obtained. The mutant endo-β-1,3-glucanase showed efficient specific activities for degrading curdlan (366 U mg^-1) and scleroglucan (274.5 U mg^-1). Thereafter, one-step production of functional branched oligoglucosides was established with coupled fermentation of Pichia pastoris and Sclerotium rolfsii. During the fermentation process, the endo-β-1,3-glucanase secreted by Pichia pastoris GS115 can efficiently hydrolyse scleroglucan metabolized by Sclerotium rolfsii WSH-G01. The maximum yields of β-oligoglucosides in the shake flasks and 7-L bioreactor reached 1.73 g L^-1 and 12.71 g L^-1, respectively, with polymerization degrees of 2-17. The successful implementation of heterologous expression with error-prone PCR and the coupled fermentation simplified the multi-step enzymatic β-oligoglucoside preparation procedures, which makes it a potential strategy for industrial production of functional oligosaccharides.

Efficient endo-β-1,3-glucanase expression in Pichia pastoris for co-culture with Agrobacterium sp. for direct curdlan oligosaccharide production

The production of curdlan oligosaccharides, a multifunctional and valuable carbohydrate, by hydrolyzing polysaccharides is of great interest. The endo-β-1,3-glucanase derived from Trichoderma harzianum was expressed in Pichia pastoris with three commonly used promoters (AOX1, GAP and FLD1). The purified recombinant endo-β-1,3-glucanase expressed by Pichia pastoris with GAP promoter displayed high specific activity at pH 5.5 and 50 °C. Thereafter, a co-culture system of Pichia pastoris GS115 (GAP promoter) and Agrobacterium sp. was constructed in which Agrobacterium sp.-metabolized curdlan can be directly hydrolyzed by Pichia pastoris-secreted endo-β-1,3-glucanase to produce functional curdlan oligosaccharides. The co-culture conditions were optimized and the process was carried out in a 7-L bioreactor. The maximum yield of curdlan oligosaccharides reached 18.77 g/L with 3-10 degrees of polymerization. This study presents a novel and easy curdlan oligosaccharide production strategy that can replace traditional sophisticated production procedures and could potentially be implemented for production of other oligosaccharides.

Synthesis of functional oligosaccharides and their derivatives through cocultivation and cellular NTP regeneration

Carbohydrates play an important role in the life cycle. Among them, functional oligosaccharides show a complex and diverse structures with unique physiological activities and biological functions. However, different preparation methods directly affect the structure, molecular weight, and other functions of oligosaccharides, as well as their application fields and manufacturing costs. In the preparation of β-1,3-glucan oligosaccharides (OBGs), water insolubility of β-1,3-glucans hampers the hydrolysis efficiency. The synthesis of some functional oligosaccharides requires the consumption of energy substrates, such as ATP, CTP, and uridine triphosphate, for sugar nucleotide synthesis, leading to increased capital costs. A more economical solution to solve energy supply is to adopt microbial cocultivation or cellular nucleoside triphosphate regeneration. This review focused on the sources, preparation methods, biological activities of OBG, and the cultivation methods and applications of microbial cocultivation and fermentation. We also reviewed the preparation methods of other functional oligosaccharides, such as sialylated oligosaccharides, β-nicotinamide mononucleotide, and α-galacto-oligosaccharides.

Biochemical Characterization of a Novel Endo-1,3-β-Glucanase from the Scallop Chlamys farreri

Endo-1,3-β-glucanases derived from marine mollusks have attracted much attention in recent years because of their unique transglycosylation activity. In this study, a novel endo-1,3-β-glucanase from the scallop Chlamys farreri, named L_cf, was biochemically characterized. Unlike in earlier studies on marine mollusk endo-1,3-β-glucanases, L_cf was expressed in vitro first. Enzymatic analysis demonstrated that L_cf preferred to hydrolyze laminarihexaose than to hydrolyze laminarin. Furthermore, L_cf was capable of catalyzing transglycosylation reactions with different kinds of glycosyl acceptors. More interestingly, the transglycosylation specificity of L_cf was different from that of other marine mollusk endo-1,3-β-glucanases, although they share a high sequence identity. This study enhanced our understanding of the diverse enzymatic specificities of marine mollusk endo-1,3-β-glucanases, which facilitated development of a unique endo-1,3-β-glucanase tool in the synthesis of novel glycosides.

Molecular dynamic simulation: Conformational properties of single-stranded curdlan in aqueous solution

Recently, molecular dynamic simulation technique has been proved to be a powerful tool providing structural insights for better understanding the functionality of carbohydrates. Here, by using molecular dynamic simulation method we investigated the detailed conformational properties of the single-stranded curdlan with 12 glucose units. The results showed that the right-handed 6/1 helix structure was thermodynamically the most stable conformation in solution. The formation of the helix conformation was determined by many factors such as the glycosidic linkage, explicit water solvation and hydrogen bonds. When temperature was increased, the representative helix conformation was found becoming unstable giving rise to metastable conformations because when water mobility was accelerated with temperature, the hydrogen bonding strength between the curdlan chain and water went down, breaking the continuity of the hydrogen bonding network of water and hydroxyl groups. When the number of repeating glucose units varied from 6 to 24, the major helix conformation remained, but the conformational properties of longer chains were more apparently aff ;ected by chain flexibility.

Effects of carbon sources on production and properties of curdlan using Agrobaterium sp. DH-2

Curdlan has wide potential application in the food and biomedical fields due to its unique thermal gel and biological activity. This study investigated the effect of six sugars including glucose, fructose, lactose, maltose, sucrose and xylose as carbon sources on production and properties of curdlan using Agrobacterium sp. DH-2. The maximum production (38.1 g/L and 37.4 g/L, respectively) and yield (0.58 g curdlan/g sucrose and 0.53 g curdlan/g maltose, respectively) of curdlan were achieved by sucrose and maltose, followed by glucose, fructose, lactose and xylose. Scanning electron micrographs showed that the surface of cells was smooth in strain growth phase, while cells were covered by curdlan matrix acted as a net in the curdlan synthesis phase. The highest glucosyltransferase activity (19.9 U/g biomass) corresponded to the maximum curdlan production using the sucrose medium. The molecular weight and gel strength of curdlan were influenced by the carbon sources. The curdlan from xylose medium resulted in a maximum molecular weight of 1.59 × 10⁶ Da and the highest gel strength of 989.2 g/cm², while the curdlan from sucrose medium resulted in a lowest molecular weight of 1.10 × 10⁶ Da and gel strength of 672.8 g/cm². The high molecular weight of curdlan had high gel strength.

Curdlan (Alcaligenes faecalis) (1→3)-β-d-Glucan Oligosaccharides Drive M1 Phenotype Polarization in Murine Bone Marrow-Derived Macrophages via Activation of MAPKs and NF-κB Pathways

Functional oligosaccharides, particularly curdlan (1→3)-β-d-glucan oligosaccharides (GOS), play important roles in modulating host immune responses. However, the molecular mechanisms underlying the immunostimulatory effects of GOS on macrophage polarization are not clear. In this work, GOS (5–1000 µg/mL) were non-toxic to bone marrow-derived macrophages (BMDMs) with improved pinocytic and bactericidal capacities. Incubation with GOS (100 µg/mL) induced M1 phenotype polarization of BMDMs as evidenced by increased CD11c⁺/CD86⁺ (10.1%) and M1 gene expression of inducible nitric oxide synthase, interleukin (IL)-1β, and chemokine C-C-motif ligand 2. Accordingly, the secretion of cytokines IL-1β, IL-6, monocyte chemotactic protein-1, and tumor necrosis factor-α, as well as the nitrite release of BMDMs were increased by GOS (100 µg/mL). Expression of mitogen-activated protein kinases (MAPKs) of phosphorylated (p)-c-Jun amino-terminal kinase, p-extracellular signal regulated kinase, and p-p38 in BMDMs were increased by GOS, as well as the p-Stat1. Moreover, nuclear factor-kappa B (NF-κB) p-p65 expression in BMDMs was promoted by GOS while it suppressed IκBα expression. Receptor blocking with anti-CR3 (CD11b/CD18) and anti-toll-like receptor (TLR) 2 antibodies diminished GOS induced M1 phenotype polarization with reduced mRNA expression of M1 genes, decreased cytokine and nitrite releases, and suppressed signaling pathway activation. Thus, CR3 (CD11b/CD18) and TLR2 mediated activation of MAPKs and NF-κB pathways are responsible for GOS induced polarization of BMDMs.

β-glucan modulates cortisol levels in stressed pacu (Piaractus mesopotamicus) inoculated with heat-killed Aeromonas hydrophila

In this study, we show that β-glucan can modulate cortisol release in fish. We simulated a common situation in aquaculture: the transport of fish followed by contact with an opportunistic pathogen and observed what effect glucan had on the immune and stress response in these conditions. Pacu (Piaractus mesopotamicus) were fed with a diet containing β-glucan (0.1%) for 15 days prior to transport followed by an injection with heat-killed Aeromonas hydrophila. We sampled fish before transport, at arrival and at 3 and 24 h after bacterial injection. β-Glucans are used in aquaculture and have a known immunostimulatory effect, which was observed in this study. The results showed that β-glucan modulated the plasma cortisol levels differently by increasing these levels up to 24 h after transport and preventing the increase caused by bacterial inoculum injection. In addition, β-glucan enhanced the activity of the complement system at 24 h and reduced the monocytes and lymphocytes number in peripheral blood at 3 and 24 h after bacterial inoculation. Our results suggest that β-glucan modulated a bidirectional interaction between the stress and the immune responses. The modulation of cortisol levels and the immunostimulation by β-glucan at different moments in our study suggest the compound has a protective effect by avoiding higher levels of the hormone and improving resistance against bacterial infection in pacu. These results add evidence to support the use of β-glucan as an immunomodulator in the aquaculture industry.

β-Glucan Grafted Microcapsule, a Tool for Studying the Immunomodulatory Effect of Microbial Cell Wall Polysaccharides

β-(1,3)-Glucan is one of the antigenic components of the bacterial as well as fungal cell wall. We designed microcapsules (MCs) ligated with β-(1,3)-glucan, to study its immunomodulatory effect. The MCs were obtained by interfacial polycondensation between diacyl chloride (sebacoyl chloride and terephtaloyl chloride) and diethylenetriamine in organic and aqueous phases, respectively. Planar films were first designed to optimize monomer compositions and to examine the kinetics of film formation. MCs with aqueous fluorescent core were then obtained upon controlled emulsification-polycondensation reactions using optimized monomer compositions and adding fluorescein into the aqueous phase. The selected MC-formulation was grafted with Curdlan, a linear β-(1,3)-glucan from  Agrobacterium species or branched β-(1,3)-glucan isolated from the cell wall of Aspergillus fumigatus. These β-(1,3)-glucan grafted MCs were phagocytosed by human monocyte-derived macrophages, and stimulated cytokine secretion. Moreover, the blocking of dectin-1, a β-(1,3)-glucan recognizing receptor, did not completely inhibit the phagocytosis of these β-(1,3)-glucan grafted MCs, suggesting the involvement of other receptors in the recognition and uptake of β-(1,3)-glucan. Overall, grafted MCs are a useful tool for the study of the mechanism of phagocytosis and immunomodulatory effect of the microbial polysaccharides.

Protein components of water extracts from fruiting bodies of the reishi mushroom Ganoderma lucidum contribute to the production of functional molecules

BACKGROUND

Mushrooms have been widely considered as health foods as their extracts have anti-hypertensive and anti-tumor activities. After a thorough literature survey, we hypothesized that enzymes in mushroom extracts play an important role in synthesizing functional molecules. Therefore, in this study, proteins extracted from reishi mushroom (Ganoderma lucidum), which is used in oriental medicine, were identified by the proteomic approach, and appropriate extraction methods for improving angiotensin-converting enzyme (ACE) inhibitory activities were investigated.

RESULTS

Various glycoside hydrolases (GHs), such as β-N-acetylhexosaminidase (GH family 20), α-1,2-mannosidase (GH family 47), endo-β-1,3-glucanase (GH family 128), and β-1,3-glucanase (GH152), that degrade glycans in the fruiting body were identified. The residual glucanase activities generated β-oligosaccharides. Additionally, the glutamic acid protease of the peptidase G1 family was determined as the major protein in the extract, and the residual peptidase activity of the extracts was found to improve ACE inhibitory activities. Finally, it was observed that extraction at 50 °C is suitable for yielding functional molecules with high ACE inhibitory activities.

CONCLUSION

Water extraction is generally believed to extract only functional macromolecules that exist in mushroom fruiting bodies. This study proposed a new concept that describes how functional molecules are produced by enzymes, including proteases and GHs, during extraction. © 2018 Society of Chemical Industry.

Isolation of β-1,3-Glucanase-Producing Microorganisms from Poria cocos Cultivation Soil via Molecular Biology

β-1,3-Glucanase is considered as a useful enzymatic tool for β-1,3-glucan degradation to produce (1→3)-linked β-glucan oligosaccharides with pharmacological activity properties. To validly isolate β-1,3-glucanase-producing microorganisms, the soil of Wolfiporia extensa, considered an environment rich in β-1,3-glucan-degrading microorganisms, was subjected to high throughput sequencing. The results demonstrated that the genera Streptomyces (1.90%) and Arthrobacter (0.78%) belonging to the order Actinomycetales (8.64%) in the phylum Actinobacteria (18.64%) were observed in soil for P. cocos cultivation (FTL₁). Actinomycetes were considered as the candidates for isolation of glucan-degrading microorganisms. Out of 58 isolates, only 11 exhibited β-1,3-glucan-degrading activity. The isolate SYBCQL belonging to the genus Kitasatospora with β-1,3-glucan-degrading activity was found and reported for the first time and the isolate SYBC17 displayed the highest yield (1.02 U/mg) among the isolates. To check the β-1,3-glucanase contribution to β-1,3-glucan-degrading activity, two genes, 17-W and 17-Q, encoding β-1,3-glucanase in SYBC17 and one gene QLK1 in SYBCQL were cloned and expressed for verification at the molecular level. Our findings collectively showed that the isolates able to secrete β-1,3-glucanase could be obtained with the assistance of high-throughput sequencing and genes expression analysis. These methods provided technical support for isolating β-1,3-glucanase-producing microorganisms.

Determination of Curdlan Oligosaccharides with High-Performance Anion Exchange Chromatography with Pulsed Amperometric Detection

The increasing interest of curdlan oligosaccharides (COS) in medicine and plant protection fields implies a necessity to identify and quantify this product. In the present study, an efficient and sensitive analytical method based on high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was established for the simultaneous separation and determination of D-glucose and ß-1,3-linked COS ranging from (COS)₂ to (COS)₆ within 20 min. Detection limits were 0.01 to 0.03 mg/L. The optimized assay was performed on a CarboPac-PA100 analytical column (4 mm × 250 mm) using isocratic elution with water-0.2 M sodium hydroxide-0.5 M sodium acetate mixture (50 : 30 : 20, v/v/v) as the mobile phase at a flow rate of 0.8 mL/min. Regression equations indicated a good linear relationship (R ² = 0.9992-1.0000, n = 6) within the test ranges. Quality parameters including precision and accuracy were fully validated and found to be satisfactory. More important, the regression of natural logarithm values of retention times (log₁₀ RT) versus the degree polymerization (DP), as well as the slope coefficient of each COS's linear equation versus the corresponding DP, fitted a linear relationship well. These inherent linear relationships could provide valuable information to tentatively identify and quantify the COS even with the DP more than 6 without authentic standard. Furthermore, when the log₁₀ RT was plotted against log₁₀ flow rate for each COS, a perfect linear relationship was also observed.

Differential gene expression following TLR stimulation in rag1-/- mutant zebrafish tissues and morphological descriptions of lymphocyte-like cell populations

In the absence of lymphocytes, rag1-/- mutant zebrafish develop protective immunity to bacteria. In mammals, induction of protection by innate immunity can be mediated by macrophages or natural killer (NK) cells. To elucidate potential responsive cell populations, we morphologically characterized lymphocyte-like cells (LLCs) from liver, spleen and kidney hematopoietic tissues. In fish, these cells include NK cells and Non-specific cytotoxic cells (NCCs). We also evaluated the transcriptional expression response of select genes that are important indicators of NK and macrophage activation after exposure to specific TLR ligands. The LLC cell populations could be discriminated by size and further discriminated by the presence of cytoplasmic granules. Expression levels of mx, tnfα, ifnγ, t-bet and nitr9 demonstrated dynamic changes in response to intra-coelomically administered β glucan (a TLR2/6 ligand), Poly I:C (a TLR3 ligand) and resiquimod (R848) (a TLR7/8 ligand). Following TLR 2/6 stimulation, there was a greater than 100 fold increase in ifnγ in liver, kidney and spleen and moderate increases in tnfα in liver and kidney. TLR3 stimulation caused broad up regulation of mx, down-regulation of tnfα in kidney and spleen tissues and up regulation of nitr9 in the kidney. Following TLR 7/8 stimulation, there was a greater than 100 fold increase in ifnγ in liver and kidney and t-bet in liver. Our gene expression findings suggest that LLCs and macrophages are stimulated following β glucan exposure. Poly I:C causes type I interferon response and mild induction of LLC in the kidney and R-848 exposure causes the strongest LLC stimulation. Overall, the strongest NK like gene expression occurred in the liver. These differential effects of TLR ligands in rag1-/- mutant zebrafish shows strong NK cell-like gene expression responses, especially in the liver, and provides tools to evaluate the basis for protective immunity mediated by the innate immune cells of fish.

Toll-like receptor 4-related immunostimulatory polysaccharides: Primary structure, activity relationships, and possible interaction models

Toll-like receptor (TLR) 4 is an important polysaccharide receptor; however, the relationships between the structures and biological activities of TLR4 and polysaccharides remain unknown. Many recent findings have revealed the primary structure of TLR4/MD-2-related polysaccharides, and several three-dimensional structure models of polysaccharide-binding proteins have been reported; and these models provide insights into the mechanisms through which polysaccharides interact with TLR4. In this review, we first discuss the origins of polysaccharides related to TLR4, including polysaccharides from higher plants, fungi, bacteria, algae, and animals. We then briefly describe the glucosidic bond types of TLR4-related heteroglycans and homoglycans and describe the typical molecular weights of TLR4-related polysaccharides. The primary structures and activity relationships of polysaccharides with TLR4/MD-2 are also discussed. Finally, based on the existing interaction models of LPS with TLR4/MD-2 and linear polysaccharides with proteins, we provide insights into the possible interaction models of polysaccharide ligands with TLR4/MD-2. To our knowledge, this review is the first to summarize the primary structures and activity relationships of TLR4-related polysaccharides and the possible mechanisms of interaction for TLR4 and TLR4-related polysaccharides.

Gut microbiota, the pharmabiotics they produce and host health

A healthy gut microbiota plays many crucial functions in the host, being involved in the correct development and functioning of the immune system, assisting in the digestion of certain foods and in the production of health-beneficial bioactive metabolites or 'pharmabiotics'. These include bioactive lipids (including SCFA and conjugated linoleic acid) antimicrobials and exopolysaccharides in addition to nutrients, including vitamins B and K. Alterations in the composition of the gut microbiota and reductions in microbial diversity are highlighted in many disease states, possibly rendering the host susceptible to infection and consequently negatively affecting innate immune function. Evidence is also emerging of microbially produced molecules with neuroactive functions that can have influences across the brain-gut axis. For example, γ-aminobutyric acid, serotonin, catecholamines and acetylcholine may modulate neural signalling within the enteric nervous system, when released in the intestinal lumen and consequently signal brain function and behaviour. Dietary supplementation with probiotics and prebiotics are the most widely used dietary adjuncts to modulate the gut microbiota. Furthermore, evidence is emerging of the interactions between administered microbes and dietary substrates, leading to the production of pharmabiotics, which may directly or indirectly positively influence human health.

Transcriptional regulation of cytokines in the intestine of Atlantic cod fed yeast derived mannan oligosaccharide or β-glucan and challenged with Vibrio anguillarum

Immunomodulatory feed additives are expected to exert their primary influence at the intestinal level through the expression of cytokines, which in turn affect the immune responses in fish. In two separate experiments a yeast-derived mannan oligosaccharide product (YM) or a purified β-glucan (BG) product were fed to Atlantic cod (Gadus morhua L.) for 5 weeks, after which they were bath-challenged with a bacterial pathogen--Vibrio anguillarum. The transcription of selected cytokines (proinflammatory--il1b, il8, ifng; anti-inflammatory--il10) in different intestinal segments was analysed using qPCR. In the case of YM study, the effect of the compound was observed in both the posterior intestine and rectum of Atlantic cod, upon challenge with the pathogen. iIl1b expression in the posterior intestine and rectum of post-challenge fish was significantly higher than that of pre-challenge fish. In the case of il8 the difference was confined to rectum. The expression of ifng was altered only in the anterior intestine upon YM feeding. In the BG trial, the additive had a differential effect on the expression of the cytokine genes. In anterior intestine and rectum, the purified β-glucan additive significantly elevated the expression of il1b when challenged with V. anguillarum. An effect of BG on the anti-inflammatory cytokine il10 was visible in the rectum after the pathogen challenge. The differential responses of cytokines in the intestine of fish upon exposure to V. anguillarum suggest that both mannan oligosaccharides and β-glucans impact the ability of Atlantic cod to respond to the pathogen.

Pharmacological, structural, and drug delivery properties and applications of 1,3-β-glucans

1,3-β-Glucans are a class of natural polysaccharides with unique pharmacological properties and the ability to form single- and triple-helical structures that can be formed into resilient gels with the application of heat and humidity. The pharmacological capabilities of 1,3-β-glucans include the impartation of tumor inhibition, resistance to infectious disease, and improvements in wound healing. Curdlan is a linear 1,3-β-glucan that has been used extensively to study the nature of these helical structures and gels, and Curdlan sulfates have found ongoing application in the inhibition of HIV infection. 1,3-β-Glucan gels have been used in food science as stabilizers and encapsulating agents, in nanoscience as scaffolds to build nanofibers and nanowires, and in drug delivery to form nanoparticles and create helical micelles encapsulating polynucleotides. 1,3-β-Glucans are beginning to have enormous significance due to their dual nature as structure-forming agents and pharmacological substances, and research is especially focused on the application of these polymers in animal nutrition and drug delivery.

Association of beta-glucan endogenous production with increased stress tolerance of intestinal lactobacilli

The exopolysaccharide beta-glucan has been reported to be associated with many health-promoting and prebiotic properties. The membrane-associated glycosyltransferase enzyme (encoded by the gtf gene), responsible for microbial beta-glucan production, catalyzes the conversion of sugar nucleotides into beta-glucan. In this study, the gtf gene from Pediococcus parvulus 2.6 was heterologously expressed in Lactobacillus paracasei NFBC 338. When grown in the presence of glucose (7%, wt/vol), the recombinant strain (pNZ44-GTF(+)) displayed a "ropy" phenotype, while scanning electron microscopy (SEM) revealed strands of polysaccharide-linking neighboring cells. Beta-glucan biosynthesis was confirmed by agglutination tests carried out with Streptococcus pneumoniae type 37-specific antibodies, which specifically detect glucan-producing cells. Further analysis showed a approximately 2-fold increase in viscosity in broth media for the beta-glucan-producing strain over 24 h compared to the control strain, which did not show any significant increase in viscosity. In addition, we analyzed the ability of beta-glucan-producing Lactobacillus paracasei NFBC 338 to survive both technological and gastrointestinal stresses. Heat stress assays revealed that production of the polysaccharide was associated with significantly increased protection during heat stress (60-fold), acid stress (20-fold), and simulated gastric juice stress (15-fold). Bile stress assays revealed a more modest but significant 5.5-fold increase in survival for the beta-glucan-producing strain compared to that of the control strain. These results suggest that production of a beta-glucan exopolysaccharide by strains destined for use as probiotics may afford them greater performance/protection during cultivation, processing, and ingestion. As such, expression of the gtf gene may prove to be a straightforward approach to improve strains that might otherwise prove sensitive in such applications.