Mechanisms of utilisation of arabinoxylans by a porcine faecal inoculum: competition and co-operation

Effect of glycoside hydrolase-mediated wheat arabinoxylan hydrolysate on gut microbiota and metabolite profiles

Cereal arabinoxylans (AX) are complex non-digestible polysaccharides and their molecular structural features significantly influence their degradation and metabolic behaviors within the body. This study focuses on investigating the impact of wheat AX hydrolysates produced by different glycoside hydrolases on the gut microbiota during colonic fermentation. Endo-1,4-β-xylanase (XYN) and arabinofuranosidase (ARF) were used to hydrolyze the xylan backbone and remove the arabinose side chains, respectively. The digestive and degradation fate was analyzed through in vitro simulated gastrointestinal digestion and colonic fermentation models. Results indicated that all hydrolase-treated groups exhibited different intestinal flora community structures, characterized by enhanced diversity and reduced richness of gut microbiota, along with differentially enriched bacterial taxa compared to native AX. The glycosidase-treated group showed greater advantages in promoting the growth of beneficial bacteria such as Bacteroides, Ruminococcus, and Faecalibacterium and produced higher levels of beneficial metabolites, mainly acetate, butyrate and caproate. Lower degrees of polymerization and side-chain substitution in AX enzymatic hydrolysate, along with higher levels of arabinoxylan-oligosaccharides (AXOS) exhibited the optimal promotion effects. However, certain gut bacteria such as Prevotella and Bifidobacterium prefer structurally intact long-chain AX. This study demonstrates that AX hydrolysates with different molecular characteristics, induced by specific hydrolases selectively influence distinct microbial consortia. Higher levels of short-chain unsubstituted XOS are more effective at promoting intestinal health and maintaining intestinal homeostasis.

A methyl esterase from Bifidobacterium longum subsp. longum reshapes the prebiotic properties of apple pectin by triggering differential modulatory capacity in faecal cultures

Pectin structures have received increasing attention as emergent prebiotics due to their capacity to promote beneficial intestinal bacteria. Yet the collective activity of gut bacterial communities to cooperatively metabolize structural variants of this substrate remains largely unknown. Herein, the characterization of a pectin methylesterase, BpeM, from Bifidobacterium longum subsp. longum, is reported. The purified enzyme was able to remove methyl groups from highly methoxylated apple pectin, and the mathematical modelling of its activity enabled to tightly control the reaction conditions to achieve predefined final degrees of methyl-esterification in the resultant pectin. Demethylated pectin, generated by BpeM, exhibited differential fermentation patterns by gut microbial communities in in vitro mixed faecal cultures, promoting a stronger increase of bacterial genera associated with beneficial effects including Lactobacillus, Bifidobacterium and Collinsella. Our findings demonstrate that controlled pectin demethylation by the action of a B. longum esterase selectively modifies its prebiotic fermentation pattern, producing substrates that promote targeted bacterial groups more efficiently. This opens new possibilities to exploit biotechnological applications of enzymes from gut commensals to programme prebiotic properties.

Changes in the structural, physicochemical and functional properties and in vitro fecal fermentation characteristics of barley dietary fiber fermented by Lactiplantibacillus plantarum dy-1

Fermentation is an effective method for improving the nutritional quality and functional characteristics of grains. This study investigated changes in the structural, physicochemical, and functional properties of fermented barley dietary fiber (FBDF) exerted by Lactiplantibacillus plantarum dy-1 (Lp. plantarum dy-1) as well as its in vitro fecal fermentation characteristics. Lp. plantarum dy-1 fermentation remarkably changed the structure of FBDF, including the microstructure and monosaccharide components, correlating with improved water or oil retaining and cholesterol adsorption capacities. Additionally, Lp. plantarum dy-1 fermentation significantly (p < 0.05) promoted the release of bound phenolics from 6.24 mg g-1 to 6.93 mg g-1 during in vitro digestion, contributing to the higher antioxidant capacity and inhibitory activity of α-amylase and pancreatic lipase compared with those of raw barley dietary fiber (RBDF). A total of 14 phenolic compounds were detected in the supernatants of digestion and fermentation samples. During colonic fermentation, FBDF significantly increased the production of acetate, propionate, and butyrate (p < 0.05), inhibited the growth of Escherichia-Shigella, and promoted the abundance of SCFA-producing microbiota such as Faecalibacterium and Prevotella_9. In conclusion, Lp. plantarum dy-1 fermentation enhanced the physicochemical properties and in vitro fermentation characteristics of barley dietary fiber, representing a promising bioprocessing technology for modifying barley bran.

Insights into the fermentation patterns of wheat bran cell wall polysaccharides using an in-vitro batch fermentation model

We aimed to study the structural characteristics and fermentation properties of wheat bran cell wall polysaccharides (CWPs). Sequential extractions of CWPs from wheat bran produced the water-extractable (WE) and alkali-extractable (AE) fractions. The extracted fractions were structurally characterized based on their molecular weight (Mw) and monosaccharide composition. Our findings revealed that the Mw and the ratio of arabinose to xylose (A/X) of AE were higher than those of WE and that the two fractions were mainly composed of arabinoxylans (AXs). The substrates were then subjected to in vitro fermentation by human fecal microbiota. As fermentation progressed, the total carbohydrates of WE were significantly more utilized than that of AE (p < 0.05). The AXs in WE were utilized at a higher rate than those in AE. The relative abundance of Prevotella_9, which can efficiently utilize AXs, was significantly increased in AE. The presence of AXs in AE shifted the balance away from protein fermentation and caused a delay in protein fermentation. Our study demonstrated that wheat bran CWPs can modulate the gut microbiota in a structure-dependent manner. However, future studies should further characterize the fine structure of wheat CWPs to clarify their detailed relationship with gut microbiota and metabolites.

A holobiont approach towards polysaccharide degradation by the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis

BACKGROUND

Termites are among the most successful insects on Earth and can feed on a broad range of organic matter at various stages of decomposition. The termite gut system is often referred to as a micro-reactor and is a complex structure consisting of several components. It includes the host, its gut microbiome and fungal gardens, in the case of fungi-growing higher termites. The digestive tract of soil-feeding higher termites is characterised by radial and axial gradients of physicochemical parameters (e.g. pH, O₂ and H₂ partial pressure), and also differs in the density and structure of residing microbial communities. Although soil-feeding termites account for 60% of the known termite species, their biomass degradation strategies are far less known compared to their wood-feeding counterparts.

RESULTS

In this work, we applied an integrative multi-omics approach for the first time at the holobiont level to study the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis. We relied on 16S rRNA gene community profiling, metagenomics and (meta)transcriptomics to uncover the distribution of functional roles, in particular those related to carbohydrate hydrolysis, across different gut compartments and among the members of the bacterial community and the host itself. We showed that the Labiotermes gut was dominated by members of the Firmicutes phylum, whose abundance gradually decreased towards the posterior segments of the hindgut, in favour of Bacteroidetes, Proteobacteria and Verrucomicrobia. Contrary to expectations, we observed that L. labralis gut microbes expressed a high diversity of carbohydrate active enzymes involved in cellulose and hemicelluloses degradation, making the soil-feeding termite gut a unique reservoir of lignocellulolytic enzymes with considerable biotechnological potential. We also evidenced that the host cellulases have different phylogenetic origins and structures, which is possibly translated into their different specificities towards cellulose. From an ecological perspective, we could speculate that the capacity to feed on distinct polymorphs of cellulose retained in soil might have enabled this termite species to widely colonise the different habitats of the Amazon basin.

CONCLUSIONS

Our study provides interesting insights into the distribution of the hydrolytic potential of the highly compartmentalised higher termite gut. The large number of expressed enzymes targeting the different lignocellulose components make the Labiotermes worker gut a relevant lignocellulose-valorising model to mimic by biomass conversion industries.

2D-HSQC-NMR-Based Screening of Feruloylated Side-Chains of Cereal Grain Arabinoxylans

Arabinoxylans of commelinid monocots are characterized by high contents of ferulic acid that is incorporated into arabinose-bearing side-chains of varying complexity. Species-related differences in the feruloylated side-chain profiles of grain arabinoxylans are observed and lead to differences in arabinoxylan functionality. Here, a semi-quantitative assay based on ¹H-¹³C-correlation NMR spectroscopy (HSQC experiment) was developed to profile feruloylated side-chains of cereal grain arabinoxylans. Following acidic liberation of the feruloylated side-chains from the xylan backbone and a clean-up step using C18 solid phase extraction, the feruloylated oligosaccharides FA (5-O-trans-feruloyl-L-arabinofuranose), FAX (β-d-xylopyranosyl-(1 → 2)-5-O-trans-feruloyl-l-arabinofuranose) and FAXG (α-l-galactopyranosyl-(1 → 2)-β-d-xylopyranosyl-(1 → 2)-5-O-trans-feruloyl-l-arabinofuranose) were analyzed by HSQC-NMR. Marker signals were identified for each compound, and experimental conditions such as solvent and internal standard as well as measurement and processing conditions were optimized for a semi-quantitative determination. The approach was validated with respect to accuracy, precision, limit of detection, and limit of quantification. The newly developed approach was applied to several cereal samples including oats, popcorn maize, wheat, and wild rice. Data were compared to an HPLC-DAD/MS approach published earlier by our group, demonstrating that the results of the HSQC approach were comparable to the more time-consuming and technically more challenging HPLC-DAD/MS method.

Intestinal microbiota and its interaction to intestinal health in nursery pigs

The intestinal microbiota has gained increased attention from researchers within the swine industry due to its role in promoting intestinal maturation, immune system modulation, and consequently the enhancement of the health and growth performance of the host. This review aimed to provide updated scientific information on the interaction among intestinal microbiota, dietary components, and intestinal health of pigs. The small intestine is a key site to evaluate the interaction of the microbiota, diet, and host because it is the main site for digestion and absorption of nutrients and plays an important role within the immune system. The diet and its associated components such as feed additives are the main factors affecting the microbial composition and is central in stimulating a beneficial population of microbiota. The microbiota–host interaction modulates the immune system, and, concurrently, the immune system helps to modulate the microbiota composition. The direct interaction between the microbiota and the host is an indication that the mucosa-associated microbiota can be more effective in evaluating its effect on health parameters. It was demonstrated that the mucosa-associated microbiota should be evaluated when analyzing the interaction among diets, microbiota, and health. In addition, supplementation of feed additives aimed to promote the intestinal health of pigs should consider their roles in the modulation of mucosa-associated microbiota as biomarkers to predict the response of growth performance to dietary interventions.

In vitro Colon Fermentation of Soluble Arabinoxylan Is Modified Through Milling and Extrusion

Dietary fibers such as arabinoxylan (AX) are promising food constituents to prevent particular diet-related chronic diseases because of their prebiotic properties. Arabinoxylan fermentation by the gut microbiota depends on the structural architecture of AX, which can be modified during food processing and consequently affect its prebiotic potential, but it is little investigated. Therefore, the aim of this study was to evaluate the effects of naturally occurring and processing-induced structural alterations of the soluble AX of wheat bran and rye flour on the in vitro human colon fermentation. It was found that fermentation behavior is strongly linked to the AX fine structure and their processing-induced modifications. The short-chain fatty acid (SCFA) metabolism, acidification kinetics, bacterial growth, and bacterial composition revealed that wheat bran AX (WBAX) was fermented faster than rye flour AX. Increased levels of bound phenolic acids resulting from processing were identified as the inhibiting factor for AX fermentation kinetics. Bacterial genera promoted by AX varied between AX source and processing type, but also between microbiota. Extruded WBAX promoted butyrate production and growth of butyrate-producing Faecalibacterium in the butyrogenic microbiota while it did not enhance fermentation and inhibited the growth of Prevotella in the propiogenic microbiota. We anticipate that the findings of this study are a starting point for further investigation on the impact of processing-induced changes on the prebiotic potential of dietary fibers prior to human studies.

The influence of xylanase on the fermentability, digestibility, and physicochemical properties of insoluble corn-based fiber along the gastrointestinal tract of growing pigs

In theory, supplementing xylanase in corn-based swine diets should improve nutrient and energy digestibility and fiber fermentability, but its efficacy is inconsistent. The experimental objective was to investigate the impact of xylanase on energy and nutrient digestibility, digesta viscosity, and fermentation when pigs are fed a diet high in insoluble fiber (>20% neutral detergent fiber; NDF) and given a 46-d dietary adaptation period. A total of 3 replicates of 20 growing gilts were blocked by initial body weight, individually housed, and assigned to 1 of 4 dietary treatments: a low-fiber control (LF) with 7.5% NDF, a 30% corn bran high-fiber control (HF; 21.9% NDF), HF + 100 mg xylanase/kg (HF + XY [Econase XT 25P; AB Vista, Marlborough, UK]) providing 16,000 birch xylan units/kg; and HF + 50 mg arabinoxylan-oligosaccharide (AXOS) product/kg (HF + AX [XOS 35A; Shandong Longlive Biotechnology, Shandong, China]) providing AXOS with 3–7 degrees of polymerization. Gilts were allowed ad libitum access to fed for 36-d. On d 36, pigs were housed in metabolism crates for a 10-d period, limit fed, and feces were collected. On d 46, pigs were euthanized and ileal, cecal, and colonic digesta were collected. Data were analyzed as a linear mixed model with block and replication as random effects, and treatment as a fixed effect. Compared with LF, HF reduced the apparent ileal digestibility (AID), apparent cecal digestibility (ACED), apparent colonic digestibility (ACOD), and apparent total tract digestibility (ATTD) of dry matter (DM), gross energy (GE), crude protein (CP), acid detergent fiber (ADF), NDF, and hemicellulose (P < 0.01). Relative to HF, HF + XY improved the AID of GE, CP, and NDF (P < 0.05), and improved the ACED, ACOD, and ATTD of DM, GE, CP, NDF, ADF, and hemicellulose (P < 0.05). Among treatments, pigs fed HF had increased hindgut DM disappearance (P = 0.031). Relative to HF, HF + XY improved cecal disappearance of DM (162 vs. 98 g; P = 0.008) and NDF (44 vs. 13 g; P < 0.01). Pigs fed xylanase had a greater proportion of acetate in cecal digesta and butyrate in colonic digesta among treatments (P < 0.05). Compared with LF, HF increased ileal, cecal, and colonic viscosity, but HF + XY decreased ileal viscosity compared with HF (P < 0.001). In conclusion, increased insoluble corn-based fiber decreases digestibility, reduces cecal fermentation, and increases digesta viscosity, but supplementing xylanase partially mitigated that effect.

In vitro fermentation outcomes of arabinoxylan and galactoxyloglucan depend on fecal inoculum more than substrate chemistry

Using in vitro fermentation conditions, this study investigated the fermentation characteristics of arabinoxylan (AX) and xyloglucan (XG) with a fecal inoculum that was collected either from humans consuming unrestricted diets or pigs fed a semi-defined diet with cellulose being the sole non-starch polysaccharide for 10 days prior to fecal collection. Metagenomic analysis revealed that microbial communities in the two types of inoculum were distinctively different, which led to distinct fermentation characteristics with the polysaccharides. The microbial communities fermented with the porcine fecal inoculum were clustered according to the fermentation time, while those fermented with the human fecal inoculum were differentiated by the substrates. Using the porcine fecal inoculum, irrespective of the substrates, Prevotella copri and the unclassified lineage rc4-4 were the dominant operational taxonomic units (OTUs) promoted during fermentation. Fermentation of wheat AX (WAX) and galacto-XG (GXG) with the human fecal inoculum, however, promoted different OTUs, except for a shared OTU belonging to Lachnospiraceae. Specifically, WAX promoted the growth of Bacteroides plebeius and a Blautia sp., while GXG promoted an unclassified Bacteroidales, Parabacteroides distasonis, Bacteroides uniformis and Bacteroides sp. 2. These changes in bacterial communities were in accordance with the short chain fatty acid (SCFA) production, where comparable SCFA profiles were obtained from the porcine fecal fermentation while different amounts and proportions of SCFA were acquired from fermentation of WAX and GXG with the human fecal inoculum. Altogether, this study indicated that the starting inoculum composition had a greater effect than polysaccharide chemistry in driving fermentation outcomes.

A protocol combining breath testing and ex vivo fermentations to study the human gut microbiome

This protocol describes the application of breath testing and ex vivo fermentations to study the association between breath methane and the composition and functionality of the gut microbiome. The protocol provides a useful systems biology approach for studying the gut microbiome in humans, which combines standardized methods in human breath testing and fecal sampling. The model described is accessible and easy to repeat, but its relative simplicity means that it can deviate from human physiological conditions.

Wheat cell walls and constituent polysaccharides induce similar microbiota profiles upon in vitro fermentation despite different short chain fatty acid end-product levels

Plant cell walls as well as their component polysaccharides in foods can be utilized to alter and maintain a beneficial human gut microbiota, but it is not known whether the architecture of the cell wall influences the gut microbiota population. In this study, wheat flour cell walls (WCW) were isolated and compared with their major constituents - arabinoxylan (AX), mixed linkage (1,3)(1,4)-β-glucan (MLG) and cellulose - both separately and as a physical mixture of polysaccharides (Mix) equivalent in composition to WCW. These samples underwent in vitro fermentation with a faecal inoculum from pigs fed a diet free of cereals and soluble-fibre to avoid prior adaptation to substrates. During fermentation, samples were collected for DNA extraction and 16S rRNA gene amplicon sequencing. Bioinformatics analyses revealed that the microbial communities promoted during fermentation by AX, MLG, Mix and WCW were similar at the genus level, but differed from the microbiota observed for the cellulose substrate. Differences in proportions of propionate and butyrate end-products were associated with differences in the relative levels of genera. These findings show that, in this experiment, the microbes that flourished were able to utilize diverse WCW polysaccharides alone, in mixtures or in intact cell walls in a similar way, but that different fermentation end-products were associated with AX (propionate) or MLG (butyrate) polysaccharides.

Xylanase modulates the microbiota of ileal mucosa and digesta of pigs fed corn-based arabinoxylans likely through both a stimbiotic and prebiotic mechanism

The experimental objective was to characterize the impact of insoluble corn-based fiber, xylanase, and an arabinoxylan-oligosaccharide on ileal digesta and mucosa microbiome of pigs. Three replicates of 20 gilts were blocked by initial body weight, individually-housed, and assigned to 1 of 4 dietary treatments: a low-fiber control (LF), a 30% corn bran high-fiber control (HF), HF+100 mg/kg xylanase (HF+XY), and HF+50 mg/kg arabinoxylan oligosaccharide (HF+AX). Gilts were fed their respective treatments for 46 days. On day 46, pigs were euthanized and ileal digesta and mucosa were collected. The V4 region of the 16S rRNA was amplified and sequenced, generating a total of 2,413,572 and 1,739,013 high-quality sequences from the digesta and mucosa, respectively. Sequences were classified into 1,538 mucosa and 2,495 digesta operational taxonomic units (OTU). Hidden-state predictions of 25 enzymes were made using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUST2). Compared to LF, HF increased Erysipelotrichaceae_UCG-002, and Turicibacter in the digesta, Lachnospiraceae_unclassified in the mucosa, and decreased Actinobacillus in both (Q<0.05). Relative to HF, HF+XY increased 19 and 14 of the 100 most abundant OTUs characterized from digesta and mucosa, respectively (Q<0.05). Notably, HF+XY increased the OTU_23_Faecalibacterium by nearly 6 log2-fold change, compared to HF. Relative to HF, HF+XY increased genera Bifidobacterium, and Lactobacillus, and decreased Streptococcus and Turicibacter in digesta (Q<0.05), and increased Bifidobacterium and decreased Escherichia-Shigella in the mucosa (Q<0.05). Compared to HF, HF+AX increased 5 and 6 of the 100 most abundant OTUs characterized from digesta and mucosa, respectively, (Q<0.05), but HF+AX did not modulate similar taxa as HF+XY. The PICRUST2 predictions revealed HF+XY increased gene-predictions for enzymes associated with arabinoxylan degradation and xylose metabolism in the digesta, and increased enzymes related to short-chain fatty acid production in the mucosa. Collectively, these data suggest xylanase elicits a stimbiotic and prebiotic mechanism.

Xylanase supplementation in corn-based swine diets: a review with emphasis on potential mechanisms of action

Corn is a common energy source in pig diets globally; when financially warranted, industrial corn coproducts, such as corn distiller's dried grains with solubles (DDGS), are also employed. The energy provided by corn stems largely from starch, with some contribution from protein, fat, and non-starch polysaccharides (NSP). When corn DDGS are used in the diet, it will reduce starch within the diet; increase dietary protein, fat, and NSP levels; and alter the source profile of dietary energy. Arabinoxylans (AXs) comprise the majority of NSP in corn and its coproducts. One strategy to mitigate the antinutritive effects of NSP and improve its contribution to energy is by including carbohydrases within the diet. Xylanase is a carbohydrase that targets the β-1,4-glycosidic bonds of AX, releasing a mixture of smaller polysaccharides, oligosaccharides, and pentoses that could potentially be used by the pig. Xylanase is consistently effective in poultry production and moderately consistent in wheat-based swine diets, but its efficacy in corn-based swine diets is quite variable. Xylanase has been shown to improve the digestibility of various components of swine-based diets, but this seldom translates into an improvement in growth performance. Indeed, a review of xylanase literature conducted herein suggests that xylanase improves the digestibility of dietary fiber at least 50% of the time in pigs fed corn-based diets, but only 33% and 26% of the time was there an increase in average daily gain or feed efficiency, respectively. Intriguingly, there has been an abundance of reports proposing xylanase alters intestinal barrier integrity, inflammatory responses, oxidative status, and other health markers in the pig. Notably, xylanase has shown to reduce mortality in both high and low health commercial herds. These inconsistencies in performance metrics, and unexpected health benefits, warrant a greater understanding of the in vivo mechanism(s) of action (MOA) of xylanase. While the MOA of xylanase has been postulated considerably in the literature and widely studied in in vitro settings, in wheat-based diets, and in poultry, there is a dearth of understanding of the in vivo MOA in pigs fed corn-based diets. The purpose of this review is to explore the role of xylanase in corn-based swine diets, discuss responses observed when supplemented in diets containing corn-based fiber, suggest potential MOA of xylanase, and identify critical research gaps.

Fermentation of Ferulated Arabinoxylan Recovered from the Maize Bioethanol Industry

Maize by-product from the bioethanol industry (distiller’s dried grains with solubles, DDGS) is a source of ferulated arabinoxylan (AX), which is a health-promoting polysaccharide. In the present study, AX from DDGS was fermented by a representative colonic bacterial mixture (Bifidobacterium longum, Bifidobacterium adolescentis, and Bacteroides ovatus), and the effect of the fermented AX (AX-f) on the proliferation of the cell line Caco-2 was investigated. AX was efficiently metabolized by these bacteria, as evidenced by a decrease in the polysaccharide molecular weight from 209 kDa to < 50 kDa in AX-f, the release of ferulic acid (FA) from polysaccharide chains (1.14 µg/mg AX-f), and the short-chain fatty acids (SCFA) production (277 µmol/50 mg AX). AX-f inhibited the proliferation of Caco-2 cells by 80–40% using concentrations from 125–1000 µg/mL. This dose-dependent inverse effect was attributed to the increased viscosity of the media due to the polysaccharide concentration. The results suggest that the AX-f dose range and the SCFA and free FA production are key determinants of antiproliferative activity. Using the same polysaccharide concentrations, non-fermented AX only inhibited the Caco-2 cells proliferation by 8%. These findings highlight the potential of AX recovered from the maize bioethanol industry as an antiproliferative agent once fermented by colonic bacteria.

Mechanistic insights into the structure-dependant and strain-specific utilization of wheat arabinoxylan by Bifidobacterium longum

Arabinoxylan (AX), an important dietary fiber from cereal grains, is mainly metabolised in the large intestine by gut bacteria, especially bifidobacteria. This study investigated the uptake and metabolism of wheat AX by a Bifidobacterium longum strain that could grow well with AX as the sole carbon source. The bacterial growth rate showed a significant correlation to the molecular weight (MW) of AX and its acid hydrolysates. Assessment of the key AX degrading enzymes suggested that the uptake and consumption of AX involved extracellular cleavage of xylan backbone and intracellular degradation of both the backbone and the arabinose substitution. The preference for native or partially hydrolysed AX with single substitutions and a sufficiently high MW suggested the structure-dependant uptake by the bacterial cells. Genetic analysis of B. longum showed the lack of β-xylosidase, suggesting the existence of unknown enzymes or dual/multiple-specific enzymes for hydrolysis of the non-reducing end of xylan backbone.

Compositional and functional characterisation of biomass-degrading microbial communities in guts of plant fibre- and soil-feeding higher termites

BACKGROUND

Termites are among the most successful insect lineages on the globe and are responsible for providing numerous ecosystem services. They mainly feed on wood and other plant material at different stages of humification. Lignocellulose is often a principal component of such plant diet, and termites largely rely on their symbiotic microbiota and associated enzymes to decompose their food efficiently. While lower termites and their gut flagellates were given larger scientific attention in the past, the gut lignocellulolytic bacteria of higher termites remain less explored. Therefore, in this study, we investigated the structure and function of gut prokaryotic microbiomes from 11 higher termite genera representative of Syntermitinae, Apicotermitinae, Termitidae and Nasutitermitinae subfamilies, broadly grouped into plant fibre- and soil-feeding termite categories.

RESULTS

Despite the different compositional structures of the studied termite gut microbiomes, reflecting well the diet and host lineage, we observed a surprisingly high functional congruency between gut metatranscriptomes from both feeding groups. The abundance of transcripts encoding for carbohydrate active enzymes as well as expression and diversity profiles of assigned glycoside hydrolase families were also similar between plant fibre- and soil-feeding termites. Yet, dietary imprints highlighted subtle metabolic differences specific to each feeding category. Roughly, 0.18% of de novo re-constructed gene transcripts were shared between the different termite gut microbiomes, making each termite gut a unique reservoir of genes encoding for potentially industrially applicable enzymes, e.g. relevant to biomass degradation. Taken together, we demonstrated the functional equivalence in microbial populations across different termite hosts.

CONCLUSIONS

Our results provide valuable insight into the bacterial component of the termite gut system and significantly expand the inventory of termite prokaryotic genes participating in the deconstruction of plant biomass. Video Abstract.

The role of oligosaccharides and polysaccharides of xylan and mannan in gut health of monogastric animals

Apart from its role as a digestive and absorptive organ, the gastrointestinal (GI) tract is a vital immune organ that encompasses roughly 70 % of the total immune cells of the body. As such, the physical, chemical and nutrient composition of the diet influences overall GI function, effectively as an immune organ. With the improvement in feed technology, agro-industrial co-products that are high in fibre have been widely used as a feed ingredient in the diets of pigs and poultry. Arabinoxylan (AX) and mannan are the most abundant hemicellulosic polysaccharides present in cereal grain and co-product ingredients used in the livestock industry. When monogastric animals consume diets containing high amounts of AX and mannans, stimulation of GI immune cells may occur. This involves the activation of several cellular and molecular pathways of the immune system and requires a considerable amount of energy and nutrients to be expended by the animal, which may ultimately influence overall health and growth performance of animals. Therefore, a better understanding of the role of AX and mannan in immune modulation will be helpful in modulating untoward GI immune responses, thereby minimising nutrient and energy expenditure toward this effort. This review will summarise pertinent research on the role of oligosaccharides and polysaccharides containing AX and mannans in immune modulation in order to preserve gut integrity.

Phytochemical Profile, Bioactivity, and Prebiotic Potential of Bound Phenolics Released from Rice Bran Dietary Fiber during in Vitro Gastrointestinal Digestion and Colonic Fermentation

Whole-grain dietary fiber is rich in bound-form phenolics, and the biological activity of this special structural feature has attracted increasing attention. In this study, rice bran dietary fiber (RBDF) was subjected to in vitro gastrointestinal digestion and colonic fermentation to investigate the liberation of bound phenolics and their potential activities. Bound phenolics were released at a higher ratio during colonic fermentation (27.57%) than gastrointestinal digestion (2.68%). Nine phenolic compounds were detected from the fermentation supernatants. The released phenolics showed radical scavenging activity (DPPH and ABTS assays) and α-glucosidase inhibitory activity (IC₅₀ = 19.11 μg GAE/mL). Compared with phenolics-removed RBDF (PR-RBDF), RBDF had a significantly stronger prebiotic effect on the microbes associated with diabetes (Lactobacillus spp., Akkermansia muciniphila, and Faecalibacterium prausnitzii). These findings indicate that bound phenolics may act as important functional components that could contribute to the health benefits of whole-grain dietary fiber.