Gut microbial utilization of xylan and its implication in gut homeostasis and metabolic response

Characterization of a novel cold-active β-Xylosidase from Parabacteroides distasonis and its synergistic hydrolysis of beechwood xylan

Although β-xylosidases have broad applications in fields such as food and medicine, there is limited research on cold-active β-xylosidases. This study cloned a novel cold-active β-xylosidase XYL13 from Parabacteroides distasonis. The purified XYL13 exhibited the highest activity at 40 °C, with 42 % and 25 % of its maximum activity at 4 °C and 0 °C, respectively. Meanwhile, XYL13 predominantly produces X1 while degrading X2-X6. Additionally, XYL13 showed a significant synergistic effect (18.5-fold) with endo-xylanase for degrading beechwood xylan at low temperatures. Moreover, the site-directed mutagenesis assay indicated that Ile269 and Glu621 are essential catalytic sites of XYL13. Finally, molecular docking showed that XYL13 has an excellent binding effect with X2-X6, verifying that XYL13 can effectively cut X2-X6 to produce xylose. These results highlight the potential of cold-adapted XYL13 from P. distasonis for application in the food industry.

Grain actives modulate gut microbiota to improve obesity-related metabolic diseases: A review

Whole grain diet is considered to be related to the improvement of obesity, dyslipidemia, hypertension, hyperglycemia, diabetes, and other metabolic diseases. Many studies indicate that these active ingredients in grains can act as prebiotics to improve intestinal integrity and host metabolism, preventing obesity. In this review, the physiological role of gut microbiota (GM) in the human body and its relationship with obesity were first introduced. Subsequently, the interaction between naturally derived bioactive ingredients in grains and GM was discussed, and the research progress of different grains was made in improving obesity and related metabolic diseases by regulating GM. This article provides fundamental explanations for the regulation of whole grains on obesity by GM and novel potential for the development of whole grain functional foods.

Identification of a PET hydrolytic enzyme from the human gut microbiome unveils potential plastic biodegradation in human digestive tract

Widespread use of polyethylene terephthalate (PET) plastics and their recycling challenges have led to substantial accumulation of PET wastes in global environments, with inevitable consequences for their entry into the food chains. Recent studies have increasingly documented the ingestion of microplastics by humans through food and beverages. However, the fate of these microplastics within the gastrointestinal tract, particularly the role of the human gut microbiota, remains inadequately understood. To address this knowledge gap, we employed a bioinformatics workflow integrated with functional verification to investigate the PET digestion/degradation capabilities of intestinal microorganisms. This approach identified a novel PET hydrolase-HGMP01 from the human gut metagenome, which exhibits the capacity to hydrolyze PET nanoparticles. Moreover, comprehensive exploration for HGMP01 homologues in the human gut metagenome and metatranscriptome unveil their distribution in diverse intestinal microorganisms. This study provides biochemical evidence for an unforeseen role of human gut microbiome in plastic digestion, thus holding substantial implications for human health.

Recent advances in wolfberry polysaccharides and whey protein-based biopolymers for regulating the diversity of gut microbiota and its mechanism: A review

Imbalances in gut microbiota diversity are associated with various health issues, including obesity and related disorders. There is a growing interest in developing synergistic biopolymers based on wolfberry polysaccharides and whey protein to address these problems due to their potential health benefits. This review explores recent advances in understanding how functional foods based on Lycium barbarum polysaccharides (LBP) and whey protein (WP) influence gut microbiota diversity and their underlying mechanisms. We examine the impact of these biopolymers on microbial composition and functionality, focusing on their roles in improving health by regulating gut microbiota. The combined effects of WP and LBP significantly enhance gut microbiome metabolic activities and taxonomic diversity, offering promising avenues for treating obesity and related disorders.

Lipid metabolism regulation by dietary polysaccharides with different structural properties

Lipid metabolism plays an important role in energy homeostasis maintenance in response to stress. Nowadays, hyperlipidemia-related chronic diseases such as obesity, diabetes, atherosclerosis, and fatty liver pose significant health challenges. Dietary polysaccharides (DPs) have gained attention for their effective lipid-lowering properties. This review examines the multifaceted mechanisms that DPs employ to lower lipid levels in subjects with hyperlipidemia. DPs could directly inhibit lipid intake and absorption, promote lipid excretion, and regulate key enzymes involved in lipid metabolism pathways, including triglyceride and cholesterol anabolism and catabolism, fatty acid oxidation, and bile acid synthesis. Additionally, DPs indirectly improve lipid homeostasis by modulating gut microbiota composition and alleviating oxidative stress. Moreover, the lipid-lowering mechanisms of particular structural DPs (including β-glucan, pectin, glucomannan, inulin, arabinoxylan, and fucoidan) are summarized. The relationship between the structure and lipid-lowering activity of DPs is also discussed based on current researches. Finally, potential breakthroughs and future directions in the development of DPs in lipid-lowering activity are discussed. The paper could provide a reference for further exploring the mechanism of DPs for lipid regulations and utilizing DPs as lipid-lowering dietary ingredients.

A water-soluble arabinoxylan from Chinese liquor distillers' grains: Structural characterization and anti-colitic properties

Chinese liquor distillers' grain (CLDG) is a valuable and abundant by-product from traditional Chinese baijiu production, containing a diverse array of bioactive components that have attracted significant interest. Herein, a water-soluble polysaccharide, DGPS-2B, with a weight-average molecular weight of 37.3 kDa, was isolated from the alkali-extract fraction of CLDG. Methylation and NMR analysis identified that the primary constituents of DGPS-2B are arabinoxylans, with an arabinose-to-xylose ratio of 0.66. In an animal model of colitis, DGPS-2B treatment significantly altered the gut microbiota composition by increasing the SCFA-producing bacteria (e.g., Butyricicoccus) and reducing the mucin-degrading bacteria such as Muribaculaceae. This microbial shift resulted in elevated production of butyrate, acetate, and propionate, which subsequently suppressed NF-κB signaling, decreased the levels of IL-1β, IL-6, and TNFα, and potentially inactivated Notch signaling. These multifaceted effects stimulated mucin 2 production, reduced inflammation and apoptosis in the gut epithelium, and ultimately alleviated colitis symptoms. Collectively, this study not only elucidates the purification and characterization of DGPS-2B from CLDG but also illuminates its anti-colitic properties and the underlying molecular mechanisms. These findings underscore the potential of DGPS-2B as a therapeutic intervention for managing inflammatory bowel disease and emphasize CLDG as a promising source for developing value-added products.

In vivo absorption, in vitro simulated digestion and fecal fermentation properties of polysaccharides from Pinelliae Rhizoma Praeparatum Cum Alumine and their effects on human gut microbiota

Polysaccharides from Pinelliae Rhizoma Praeparatum Cum Alumine (PPA) have various biological activities, but their properties after oral administration are not clear. In this study, the absorption, digestion and fermentation properties of PPA were studied using in vivo fluorescence tracking, in vitro simulated digestion and fecal fermentation experiments. The absorption experiment showed that fluorescence was only observed in the gastrointestinal system, indicating that PPA could not be absorbed. Simulated digestion results showed that there were no significant changes in the molecular weight, Fourier transform infrared spectroscopy (FT-IR) spectrum, monosaccharides and reducing sugar of PPA during the digestion process, showing that the overall structure of PPA was not damaged. However, the carbohydrate gel electrophoresis bands of PPA enzymatic hydrolysates after simulated digestion were significantly changed, indicating that simulated digestion might impact the configuration of PPA. In vitro fermentation showed that PPA could be degraded by microorganisms to produce short chain fatty acids, leading to a decrease in pH value. PPA can promote the proliferation of Bacteroideaceae, Megasphaera, Bacteroideaceae, and Bifidobacteriaceae, and inhibit the growth of Desulfobacteriota and Enterobacteriaceae. The results indicated that PPA could treat diseases by regulating gut microbiota, providing a scientific basis for the application and development of PPA.

Influence of chain length on the colonic fermentation of xylooligosaccharides

Xylooligosaccharides (XOS) have been employed as prebiotics containing oligomers of varying sizes or molecular ratios. XOS with a low degree of polymerization (DP) has been demonstrated to have high prebiotic potential. However, there is limited information regarding the specific chain length of XOS required to elicit distinct responses in the gut microbiota. In this study, we aimed to explore whether variations in XOS DP could alter the fate of colonic fermentation. Five XOS fractions (BWXFs) with DP ranges of >40, 20-40, 10-20, 5-10, and 2-4 were prepared by beechwood xylan autohydrolysis and tested on human gut microbiota. Extracellular XOS degradation was observed for molecules with a DP exceeding 5. BWXF treatments altered the microbial community structures, and substrate size-dependent effects on the microbial composition and metabolic outputs were observed. Bacteroidaceae were specifically enriched by xylan. Lachnospiraceae were particularly stimulated by XOS with a DP of 20-40 and 2-4. Bifidobacteriaceae were notably enriched by XOS with a DP of 5-20. High butyrate yields were obtained from cultures containing long-chain BWXFs. Microbiota responses differed with XOS DP composition changes, and microbial competition with XOS with a DP of 2-4 requires further exploration.

Comparative analysis of differential gene expression reveals novel insights into the heteroblastic foliage functional traits of Pinus massoniana seedlings

Pinus massoniana needles, rich in medicinal polysaccharides and flavonoids, undergo heteroblastic foliage, transitioning from primary needles (PN) to secondary needles (SN) during growth, resulting in altered functional traits. Despite its significance, the molecular regulatory mechanisms governing these traits remain unclear. This study employs Iso-Seq and RNA-Seq analyses to explore differentially expressed genes (DEGs) associated with functional traits throughout the main growth season of heteroblastic foliage. Co-expression network analysis identified 34 hub genes and 17 key transcription factors (TFs) influencing light-harvesting antenna, photosystem I and II, crucial in photosynthesis regulation. Additionally, 14 genes involved in polysaccharide metabolism pathways, synthesizing sucrose, glucose, UDP sugars, and xylan, along with four genes in flavonoid biosynthesis pathways, regulating p-coumaroyl-CoA, quercetin, galangin, and myricetin production, exhibited differential expression between PN and SN. Further analysis unveils a highly interconnected network among these genes, forming a pivotal cascade of TFs and DEGs. Therefore, heteroblastic changes significantly impact needle functional traits, potentially affecting the pharmacological properties of PN and SN. Thus, these genomic insights into understanding the molecular-level differences of heteroblastic foliage, thereby establishing a foundation for advancements in the pharmaceutical industry related to needle-derived products.

Synthesis and antitumor activity of bagasse xylan derivatives modified by graft-esterification and cross-linking

A crucial aspect in achieving sustainable development of biomass materials is the modification of renewable polysaccharides to create various high-value functional materials. In this paper, bagasse xylan (BX) was used as a raw material to introduce benzyl methacrylate (BMA) through graft copolymerization reaction to generate the intermediate product BX-g-BMA. Subsequently, the target product (CA-BX-g-BMA) was synthesized by catalytic esterification of BX-g-BMA with citric acid (CA) in AmimCl ionic liquid. Meanwhile, the characterization and bioactivity studies of CA-BX-g-BMA were carried out. The graft copolymerization and esterification reactions induced significant changes in the morphological structure of BX and obviously improved its thermal stability and crystallinity. The application of density functional theory (DFT), molecular electrostatic potential (MEP) and molecular docking has revealed that CA-BX-g-BMA possesses multiple active sites, strong biological activity and a strong binding affinity to 6RCF tumor protein with a binding energy of -32.26 kJ/mol. The in vitro antitumor activity of this novel derivative was tested by MTT assay, and the results showed that CA-BX-g-BMA was non-toxic to normal cells and inhibited MDA-MB-231 (breast cancer cells) by up to 32.16 % ± 4.89 %, which is approximately 11 times higher than that of BX. The exploration of these properties is essential to promote future multidisciplinary applications of BX derivatives.

Marine algal polysaccharides as future potential constituents against non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is one of the most chronic and incurable liver diseases triggered mainly by an inappropriate diet and hereditary factors which burden liver metabolic stress, and may result in liver fibrosis or even cancer. While the available drugs show adverse side effects. The non-toxic bioactive molecules derived from natural resources, particularly marine algal polysaccharides (MAPs), present significant potential for treating NASH. In this review, we summarized the protective effects of MAPs on NASH from multiple perspectives, including reducing oxidative stress, regulating lipid metabolism, enhancing immune function, preventing fibrosis, and providing cell protection. Furthermore, the mechanisms of MAPs in treating NASH were comprehensively described. Additionally, we highlight the influences of the special structures of MAPs on their bioactive differences. Through this comprehensive review, we aim to further elucidate the molecular mechanisms of MAPs in NASH and inspire insights for deeper research on the functional food and clinical applications of MAPs.

Degradation of xylan by human gut Bacteroides xylanisolvens XB1A

Although many polysaccharides utilization loci (PULs) have been investigated by genomics and transcriptomics, the detailed functional characterization lags severely behind. We hypothesize that PULs on the genome of Bacteroides xylanisolvens XB1A (BX) dictate the degradation of complex xylan. To address, xylan S32 isolated from Dendrobium officinale was employed as a sample polysaccharide. We firstly showed that xylan S32 promoted the growth of BX which might degrade xylan S32 into monosaccharides and oligosaccharides. We further showed that this degradation was performed mainly via two discrete PULs in the genome of BX. Briefly, a new surface glycan binding protein (SGBP) BX_29290^SGBP was identified, and shown to be essential for the growth of BX on xylan S32. Two cell surface endo-xylanases Xyn10A and Xyn10B cooperated to deconstruct the xylan S32. Intriguingly, genes encoding Xyn10A and Xyn10B were mainly distributed in the genome of Bacteroides spp. In addition, BX metabolized xylan S32 to produce short chain fatty acids (SCFAs) and folate. Taken together, these findings provide new evidence to understand the food source of BX and the BX-directed intervention strategy by xylan.

An insight into microbial sources, classification, and industrial applications of xylanases: A rapid review

Endo 1,4-β-d-xylanases (EC3.2.1.8) are one of the key lignocellulose hydrolyzing enzymes. Xylan, which is present in copious amounts on earth, forms the primary substrate of endo-xylanases, which can unchain the constituent monosaccharides linked via β-1,4-glycosidic bonds from the xylan backbone. Researchers have shown keen interest in the xylanases belonging to glycoside hydrolase families 10 and 11, whereas those placed in other glycoside hydrolase families are yet to be investigated. Various microbes such as bacteria and fungi harbor these enzymes for the metabolism of their lignocellulose fibers. These microbes can be used as miniature biofactories of xylanase enzymes for a plethora of environmentally benign applications in pulp and paper industry, biofuel production, and for improving the quality of food in bread baking and fruit juice industry. This review highlights the potential of microbes in production of xylanase for industrial biotechnology.

Proteomic analyses of Bacteroides ovatus and Bifidobacterium longum in xylan bidirectional culture shows sugar cross-feeding interactions

The intestinal microbiome is a community of anaerobic microorganisms whose activities significantly impact human health. Its composition can be modulated by consuming foods rich in dietary fiber, such as xylan, a complex polysaccharide that can be considered an emerging prebiotic. In this work, we evaluated how certain gut bacteria acted as primary degraders, fermenting dietary fibers, and releasing metabolites that other bacteria can further use. Different bacterial strains of Lactobacillus, Bifidobacterium, and Bacteroides were evaluated for their ability to consume xylan and interact with one another. Results from unidirectional assays gave indications of possible cross-feeding between bacteria using xylan as a carbon source. Bidirectional assays showed that Bifidobacterium longum PT4 increased its growth in the presence of Bacteroides ovatus HM222. Proteomic analyses indicated that B. ovatus HM222 synthesizes enzymes facilitating xylan degradation, such as β-xylanase, arabinosidase, L-arabinose isomerase, and xylosidase. Interestingly, the relative abundance of these proteins remains largely unaffected in the presence of Bifidobacterium longum PT4. In the presence of B. ovatus, B. longum PT4 increased the production of enzymes such as α-L-arabinosidase, L-arabinose isomerase, xylulose kinase, xylose isomerase, and sugar transporters. These results show an example of positive interaction between bacteria mediated by xylan consumption. Bacteroides degraded this substrate to release xylooligosaccharides, or monosaccharides (xylose, arabinose), which might support the growth of secondary degraders such as B. longum.

To Fiber or Not to Fiber: The Swinging Pendulum of Fiber Supplementation in Patients with Inflammatory Bowel Disease

Evidence-based dietary guidance around dietary fiber in inflammatory bowel disease (IBD) has been limited owing to insufficient reproducibility in intervention trials. However, the pendulum has swung because of our increased understanding of the importance of fibers in maintaining a health-associated microbiome. Preliminary evidence suggests that dietary fiber can alter the gut microbiome, improve IBD symptoms, balance inflammation, and enhance health-related quality of life. Therefore, it is now more vital than ever to examine how fiber could be used as a therapeutic strategy to manage and prevent disease relapse. At present, there is limited knowledge about which fibers are optimal and in what form and quantity they should be consumed to benefit patients with IBD. Additionally, individual microbiomes play a strong role in determining the outcomes and necessitate a more personalized nutritional approach to implementing dietary changes, as dietary fiber may not be as benign as once thought in a dysbiotic microbiome. This review describes dietary fibers and their mechanism of action within the microbiome, details novel fiber sources, including resistant starches and polyphenols, and concludes with potential future directions in fiber research, including the move toward precision nutrition.

In vitro simulated digestion of and microbial characteristics in colonic fermentation of polysaccharides from four varieties of Tibetan tea

Polysaccharides as a functional prebiotic have numerous activities such as regulating intestinal microorganisms and polysaccharide is one of the functional active components in tea has been known. In this study, we aimed to investigate the physicochemical characteristics of polysaccharides from four kinds of Tibetan teas at simulated digestion stages and the effect on the microbiota of fecal fermentation stages in vitro. The results revealed that Tibetan tea polysaccharides were partially digested during digestion. Additionally, during in vitro fecal microbial fermentation, Tibetan tea polysaccharides can promote the growth of some beneficial bacteria such as Bifidobacterium, Prevotella and Phascolarctobacterium to change the composition of intestinal microorganisms and promote the production of short-chain fatty acids (SCFAs). Finally, a strong correlation was found between the production of SCFAs and microorganisms including Bacteroides, Bifidobacterium and Lachnoclostridium. These results suggest that Tibetan tea polysaccharides could be developed as a prebiotic to regulate human gut microbiota.

Role of Bifidobacterium pseudocatenulatum in Degradation and Consumption of Xylan-Derived Carbohydrates

Xylans, a family of xylose-based polysaccharides, are dietary fibers resistant to digestion. They therefore reach the large intestine intact; there, they are utilized by members of the gut microbiota. They are initially broken down by primary degraders that utilize extracellular xylanases to cleave xylan into smaller oligomers. The resulting xylooligosaccharides (XOS) can either be further metabolized directly by primary degraders or cross-feed secondary consumers, including Bifidobacterium. While several Bifidobacterium species have metabolic systems for XOS, most grow poorly on longer-chain XOS and xylan substrates. In this study, we isolated strains of Bifidobacterium pseudocatenulatum and observed that some, including B. pseudocatenulatum ED02, displayed growth on XOS with a high degree of polymerization (DP) and straight-chain xylan, suggesting a primary degrader phenotype that is rare in Bifidobacterium. In silico analyses revealed that only the genomes of these xylan-fermenting (xylan+) strains contained an extracellular GH10 endo-β-1.4 xylanase, a key enzyme for primary degradation of xylan. The presence of an extracellular xylanase was confirmed by the appearance of xylan hydrolysis products in cell-free supernatants. Extracellular xylanolytic activity was only detected in xylan+ strains, as indicated by the production of XOS fragments with a DP of 2 to 6, identified by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Additionally, in vitro fecal fermentations revealed that strains with a xylan+ phenotype can persist with xylan supplementation. These results indicate that xylan+ B. pseudocatenulatum strains may have a competitive advantage in the complex environment of the gastrointestinal tract, due to their ability to act as primary degraders of xylan through extracellular enzymatic degradation. IMPORTANCE The beneficial health effects of dietary fiber are now well established. Moreover, low fiber consumption is associated with increased risks of metabolic and systemic diseases. This so-called "fiber gap" also has a profound impact on the composition of the gut microbiome, leading to a disrupted or dysbiotic microbiota. Therefore, understanding the mechanisms by which keystone bacterial species in the gut utilize xylans and other dietary fibers may provide a basis for developing strategies to restore gut microbiome function. The results described here provide biochemical and genetic evidence for primary xylan utilization by human-derived Bifidobacterium pseudocatenulatum and show also that cooperative utilization of xylans occurs among other members of this species.

Prebiotics and the Human Gut Microbiota: From Breakdown Mechanisms to the Impact on Metabolic Health

The colon harbours a dynamic and complex community of microorganisms, collectively known as the gut microbiota, which constitutes the densest microbial ecosystem in the human body. These commensal gut microbes play a key role in human health and diseases, revealing the strong potential of fine-tuning the gut microbiota to confer health benefits. In this context, dietary strategies targeting gut microbes to modulate the composition and metabolic function of microbial communities are of increasing interest. One such dietary strategy is the use of prebiotics, which are defined as substrates that are selectively utilised by host microorganisms to confer a health benefit. A better understanding of the metabolic pathways involved in the breakdown of prebiotics is essential to improve these nutritional strategies. In this review, we will present the concept of prebiotics, and focus on the main sources and nature of these components, which are mainly non-digestible polysaccharides. We will review the breakdown mechanisms of complex carbohydrates by the intestinal microbiota and present short-chain fatty acids (SCFAs) as key molecules mediating the dialogue between the intestinal microbiota and the host. Finally, we will review human studies exploring the potential of prebiotics in metabolic diseases, revealing the personalised responses to prebiotic ingestion. In conclusion, we hope that this review will be of interest to identify mechanistic factors for the optimization of prebiotic-based strategies.