Alterations in the amounts of microbial metabolites in different regions of the mouse large intestine using variably fermentable fibres

The pectin metabolizing capacity of the human gut microbiota

The human gastrointestinal microbiota, densely populated with a diverse array of microorganisms primarily from the bacterial phyla Bacteroidota, Bacillota, and Actinomycetota, is crucial for maintaining health and physiological functions. Dietary fibers, particularly pectin, significantly influence the composition and metabolic activity of the gut microbiome. Pectin is fermented by gut bacteria using carbohydrate-active enzymes (CAZymes), resulting in the production of short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate, which provide various health benefits. The gastrointestinal microbiota has evolved to produce CAZymes that target different pectin components, facilitating cross-feeding within the microbial community. This review explores the fermentation of pectin by various gut bacteria, focusing on the involved transport systems, CAZyme families, SCFA synthesis capacity, and effects on microbial ecology in the gut. It addresses the complexities of the gut microbiome's response to pectin and highlights the importance of microbial cross-feeding in maintaining a balanced and diverse gut ecosystem. Through a systematic analysis of pectinolytic CAZyme production, this review provides insights into the enzymatic mechanisms underlying pectin degradation and their broader implications for human health, paving the way for more targeted and personalized dietary strategies.

Effects of Resistant Starch Infusion, Solely and Mixed with Xylan or Cellulose, on Gut Microbiota Composition in Ileum-Cannulated Pigs

Fermentation of dietary fiber (DF) is beneficial for gut health, but its prebiotic effects are often impeded in the distal large intestine because of the fast degradation of fermentable substrates. One way to enhance the prebiotic effect of DF is to deliver fibers to the lower parts of the gut, which can be achieved by mixing different kinds of fiber. Therefore, in the present study, an ileum-cannulated pig model was employed to investigate the fermentation influence in the large intestine by infusing resistant starch solely (RS, fast fermentable fiber) and mixing with other fibers (xylan or cellulose). Twenty-four ileum-cannulated growing pigs were divided into four groups: one control group receiving saline ileal infusions and three experimental groups infused with RS, RS with xylan, or RS with cellulose. Fecal and plasma samples were analyzed for gut microbiota composition, short-chain fatty acids (SCFAs), and blood biochemistry. Results indicated no significant differences between the RS and control group for the microbiome and SCFA concentration (p > 0.05). However, RS combined with fibers, particularly xylan, resulted in enhanced and prolonged fermentation, marked by an increase in Blautia and higher lactate and acetate production (p < 0.05). In contrast, RS with cellulose infusion enriched bacterial diversity in feces (p < 0.05). Blood biochemistry parameters showed no significant differences across groups (p > 0.05), though a trend of increased glucose levels was noted in the treatment groups (p < 0.1). Overall, RS alone had a limited impact on the distal hindgut microbiota due to rapid fermentation in the proximal gut, whereas combining RS with other fibers notably improved gut microecology by extending the fermentation process.

Sex-dependent colonic microbiota modulation by hazelnut (Corylus avellana L.) dietary fiber

Although many efforts have been made to characterize the functional properties of hazelnut constituents (mainly its oil, protein, and phenolics), those of its dietary fiber (DF) have not been elucidated yet. Here, we aimed to investigate the impact of DF of natural and roasted hazelnuts, and hazelnut skin on the colonic microbiota in vivo (C57BL/6J mouse models) by determining their composition through 16S rRNA sequencing and microbial short-chain fatty acids (SCFAs) using gas chromatography. Our results revealed that hazelnut DF generally showed an acetogenic effect in male mice, whereas the same trend was not observed in the female counterparts. The 16S rRNA sequencing results showed that hazelnut DF, especially that of natural hazelnuts, increased the relative abundances of Lactobacillus-related OTUs that have probiotic potential. LEfSe analysis indicated that, for female mice, Lachnospiraceae, Prevotella, Ruminococcaceae, and Lactobacillus were found to be discriminators for DF of natural hazelnuts, roasted hazelnuts, hazelnut skin, and control, respectively, whereas Bacteroides, Lactobacillus, Prevotella, and Lactococcus were the discriminators for the male counterparts, respectively. This study clearly indicates that, although the roasting process slightly alters the functionalities, hazelnut DF favors beneficial microbes and stimulates beneficial microbial metabolites in the colon in a sex-dependent way, which could be a contributing factor to the health-promoting effects of hazelnuts. Furthermore, hazelnut skin, a byproduct of the hazelnut industry, was found to have potential to be utilized to produce functional DF targeting colonic health.

Deciphering the colonic fermentation characteristics of agavin and digestion-resistant maltodextrin in a simulated batch fermentation system

Gut microbial fermentation of soluble dietary fibers promotes general and substrate-specific health benefits. In this study, the fermentation characteristics of two soluble branched-dietary fibers, namely, agavin (a type of agave fructans) and digestion-resistant maltodextrin (RD) were investigated against cellulose, using a simulated colonic fermenter apparatus employing a mixed culture of swine fecal bacteria. After 48 h of complete fermentation period, the microbial composition was different among all groups, where Bifidobacterium spp. and Lactobacillus spp. dominated the agavin treatment, while the members of the families Lachnospiraceae and Prevotellaceae dominated the RD treatment. Agavin treatment exhibited a clearly segregated two-phased prolonged fermentation trend compared to RD treatment as manifested by the fermentation rates. Further, the highest short-chain fatty acids production even at the end of the fermentation cycle, acidic pH, and the negligible concentration of ammonia accumulation demonstrated favorable fermentation attributes of agavin compared to RD. Therefore, agavin might be an effective and desirable substrate for the colonic microbiota than RD with reference to the expressed microbial taxa and fermentation attributes. This study revealed a notable significance of the structural differences of fermentable fibers on the subsequent fermentation characteristics.

Microbial-derived antigens and metabolites in spondyloarthritis

Spondyloarthritis (SpA) is a group of chronic, immune-mediated, inflammatory diseases affecting the bone, synovium, and enthesis. Microbiome, the community of microorganisms that has co-evolved with human hosts, plays a pivotal role in human health and disease. This invisible "essential organ" supplies the host with a myriad of chemicals and molecules. In turn, microbial metabolites can serve as messengers for microbes to communicate with each other and in the cross-talk with host cells. Gut dysbiosis in SpA is associated with altered microbial metabolites, and an accumulated body of research has contributed to the understanding that changes in intestinal microbiota can modulate disease pathogenesis. We review the novel findings from human and animal studies to provide an overview of the contribution of individual microbial metabolites and antigens to SpA.

Detection and isolation of low molecular weight alginate- and laminaran-susceptible gut indigenous bacteria from ICR mice

Alginate and laminaran are the main water-soluble polysaccharides in edible brown algae such as arame Eisenia bicyclis. To determine the alginate- and/or laminaran-susceptible indigenous bacteria (SIB) in the gut, the caecal microbiomes of ICR mice fed a diet containing 2% low molecular weight (LMW ≒50 kDa) alginate or laminaran were analysed by 16S rRNA gene (V4) amplicon sequencing. At the phylum level abundances, compared to those in mice fed a no-fibre diet, Firmicutes was lower and Bacteroidetes was higher in both LMW alginate- or laminaran-fed mouse groups. At the operational taxonomic unit level, Bacteroides acidifaciens- and Bacteroides intestinalis-like bacteria were considered alginate- and laminaran-SIB, respectively. B. acidifaciens PS-4 isolated from the ICR mice fermented LMW alginate and laminaran and mainly produced succinate. B. intestinalis ALB-11 also isolated from these mice fermented laminaran and mainly produced lactate. These SIB might exert interactive effects with edible brown algal consumption and affect host health.

Lactose and Fructo-oligosaccharides Increase Visceral Sensitivity in Mice via Glycation Processes, Increasing Mast Cell Density in Colonic Mucosa

BACKGROUND & AIMS

Irritable bowel syndrome (IBS) is characterized by abdominal pain, bloating, and erratic bowel habits. A diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) can reduce symptoms of IBS, possibly by reducing microbial fermentation products. We investigated whether ingestion of FODMAPs can induce IBS-like visceral hypersensitivity mediated by fermentation products of intestinal microbes in mice.

METHODS

C57Bl/6 mice were gavaged with lactose, with or without the antiglycation agent pyridoxamine, or saline (controls) daily for 3 weeks. A separate group of mice were fed a diet containing fructo-oligosaccharides, with or without pyridoxamine in drinking water, or a normal chow diet (controls) for 6 weeks. Feces were collected and analyzed by 16S ribosomal RNA gene sequencing and bacterial community analyses. Abdominal sensitivity was measured by electromyography and mechanical von Frey filament assays. Colon tissues were collected from some mice and analyzed by histology and immunofluorescence to quantify mast cells and expression of advanced glycosylation end-product specific receptor (AGER).

RESULTS

Mice gavaged with lactose or fed fructo-oligosaccharides had increased abdominal sensitivity compared with controls, associated with increased numbers of mast cells in colon and expression of the receptor for AGER in proximal colon epithelium. These effects were prevented by administration of pyridoxamine. Lactose and/or pyridoxamine did not induce significant alterations in the composition of the fecal microbiota. Mass spectrometric analysis of carbonyl compounds in fecal samples identified signatures associated with mice given lactose or fructo-oligosaccharides vs controls.

CONCLUSIONS

We found that oral administration of lactose or fructo-oligosaccharides to mice increases abdominal sensitivity, associated with increased numbers of mast cells in colon and expression of AGER; these can be prevented with an antiglycation agent. Lactose and/or pyridoxamine did not produce alterations in fecal microbiota of mice. Our findings indicate that preventing glycation reactions might reduce abdominal pain in patients with IBS with sensitivity to FODMAPs.

Soluble Fiber and Insoluble Fiber Regulate Colonic Microbiota and Barrier Function in a Piglet Model

The main purpose of the present study was to assess the effect of soluble and insoluble fiber on colonic bacteria and intestinal barrier function in a piglet model. A total of 24 piglets (25 ± 1 d old; 7.50 ± 0.31 kg) were randomly allotted to 4 treatments: basal diet (control, CON), 1% insoluble dietary fiber (IDF) diet, 1% soluble dietary fiber (SDF) diet, and 0.5% insoluble fiber + 0.5% soluble dietary fiber (MDF) diet. The trial lasted 28 days. SDF-fed piglets showed a higher (P < 0.05) bacterial a-diversity (observed_species, chao1, and ACE) and a higher relative abundance of Proteobacteria and Actinobacteria, Solobacterium, Succinivibrio, Blautia, and Atopobium in colonic digesta than CON, IDF, and MDF groups (P < 0.05). At the same time, Bacteroidetes, Euryarchaeota, Phascolarctobacterium, Coprococcus_1, and Prevotella_1 were significantly increased in the IDF group when compared with CON, SDF, and MDF groups (P < 0.05). Furthermore, Bacteroidetes and Enterobacteriaceae, Selenomonas, Phascolarctobacterium, and Alloprevotella(P < 0.05) were significantly higher in the MDF group than those in the other three groups (P < 0.05). SDF diet increased the concentrations of short-chain fatty acid (SCFA) in colonic digesta (P < 0.05) when compared with the CON group and enhanced weight index of the colon (P < 0.05) than the CON and IDF groups. Furthermore, compared with the CON group, SDF, IDF, and MDF diets all upregulated the mRNA expressions of claudin-1 (CLDN-1) in colonic mucosa (P < 0.05), SDF and IDF diets upregulated the mRNA expressions of mucin 2 (MUC2) (P < 0.05), SDF diet increased mRNA expressions of zonula occludens 1 (ZO-1) and occludin (OCLN), while the IDF group enhanced the secretory immunoglobulin A (sIgA) concentrations (P < 0.05), respectively. IDF and MDF diets decreased expressions of TNF-α(P < 0.05). We concluded that the influence of soluble fiber on colonic microbiota was more extensive than that of insoluble fiber. Moreover, soluble fiber could more effectively improve colonic barrier function by upregulating gene expressions of the gut barrier.

Synbiotic Supplementation Containing Whole Plant Sugar Cane Fibre and Probiotic Spores Potentiates Protective Synergistic Effects in Mouse Model of IBD

Inflammatory bowel diseases (IBD) are a chronic inflammatory disorders with increasing global incidence. Synbiotic, which is a two-point approach carrying probiotic and prebiotic components in mitigating inflammation in IBD, is thought to be a pragmatic approach owing to the synergistic outcomes. In this study, the impacts of dietary supplementation with probiotic Bacillus coagulans MTCC5856 spores (B. coagulans) and prebiotic whole plant sugar cane fibre (PSCF) was assessed using a murine model of IBD. Eight-week-old C57BL/6 mice were fed a normal chow diet supplemented with either B. coagulans, PSCF or its synbiotic combination. After seven days of supplementation, colitis was induced with dextran sulfate sodium (DSS) in drinking water for seven days during the continuation of the supplemented diets. Synbiotic supplementation ameliorated disease activity index and histological score (-72%, 7.38, respectively), more effectively than either B. coagulans (-47%, 10.1) and PSCF (-53%, 13.0) alone. Synbiotic supplementation also significantly (p < 0.0001) prevented the expression of tight junction proteins and modulated the altered serum IL-1β (-40%), IL-10 (+26%), and C-reactive protein (CRP) (-39%) levels. Synbiotic supplementations also raised the short-chain fatty acids (SCFA) profile more extensively compared to the unsupplemented DSS-control. The synbiotic health outcome effect of the probiotic and prebiotic combinations may be associated with a synergistic direct immune-regulating efficacy of the components, their ability to protect epithelial integrity, stimulation of probiotic spores by the prebiotic fibre, and/or with stimulation of greater levels of fermentation of fibres releasing SCFAs that mediate the reduction in colonic inflammation. Our model findings suggest synbiotic supplementation should be tested in clinical trials.