Effect of Molecule Branching and Glycosidic Linkage on the Degradation of Polydextrose by Gut Microbiota

Polydextrose is a randomly linked complex glucose oligomer that is widely used as a sugar replacer, bulking agent, dietary fiber and prebiotic. Polydextrose is poorly utilized by the host and, during gastrointestinal transit, it is slowly degraded by intestinal microbes, although it is not known which parts of the complex molecule are preferred by the microbes. The microbial degradation of polydextrose was assessed by using a simulated model of colonic fermentation. The degradation products and their glycosidic linkages were measured by combined gas chromatography and mass spectrometry, and compared to those of intact polydextrose. Fermentation resulted in an increase in the relative abundance of non-branched molecules with a concomitant decrease in single-branched glucose molecules and a reduced total number of branching points. A detailed analysis showed a preponderance of 1,6 pyranose linkages. The results of this study demonstrate how intestinal microbes selectively degrade polydextrose, and provide an insight into the preferences of gut microbiota in the presence of different glycosidic linkages.     

Simulated colon fiber metabolome regulates genes involved in cell cycle, apoptosis, and energy metabolism in human colon cancer cells

High level of dietary fiber has been epidemiologically linked to protection against the risk for developing colon cancer. The mechanisms of this protection are not clear. Fermentation of dietary fiber in the colon results in production of for example butyrate that has drawn attention as a chemopreventive agent. Polydextrose, a soluble fiber that is only partially fermented in colon, was fermented in an in vitro colon simulator, in which the conditions mimic the human proximal, ascending, transverse, and distal colon in sequence. The subsequent fermentation metabolomes were applied on colon cancer cells, and the gene expression changes studied. Polydextrose fermentation down-regulated gene ontology classes linked with cell cycle, and affected number of metabolically active cells. Furthermore, up-regulated effects on classes linked with apoptosis, with increased caspase 2 and 3 activity, implicate that polydextrose fermentation plays a role in induction of apoptosis in colon cancer cells. The up-regulated genes involved also key regulators of lipid metabolism, such as PPARα and PGC-1α. These results offer hypotheses for the mechanisms of two health benefits linked with consumption of dietary fiber, reducing risk of development of colon cancer, and dyslipidemia.     

Effects and action mechanisms of berberine and Rhizoma coptidis on gut microbes and obesity in high-fat diet-fed C57BL/6J mice

Gut microbes play important roles in regulating fat storage and metabolism. Rhizoma coptidis (RC) and its main active compound, berberine, have either antimicrobial or anti-obesity activities. In the present study, we hypothesize that RC exerts anti-obesity effects that are likely mediated by mechanisms of regulating gut microbes and berberine may be a key compound of RC. Gut microbes and glucose and lipid metabolism in high-fat diet-fed C57BL/6J (HFD) mice in vivo are investigated after RC and berberine treatments. The results show that RC (200 mg/kg) and berberine (200 mg/kg) significantly lower both body and visceral adipose weights, and reduce blood glucose and lipid levels, and decrease degradation of dietary polysaccharides in HFD mice. Both RC and berberine significantly reduce the proportions of fecal Firmicutes and Bacteroidetes to total bacteria in HFD mice. In the trial ex vivo, both RC and berberine significantly inhibit the growth of gut bacteria under aerobic and anaerobic conditions. In in vitro trials, both RC and berberine significantly inhibit the growth of Lactobacillus (a classical type of Firmicutes) under anaerobic conditions. Furthermore, both RC and berberine significantly increase fasting-induced adipose factor (Fiaf, a key protein negatively regulated by intestinal microbes) expressions in either intestinal or visceral adipose tissues. Both RC and berberine significantly increase mRNA expressions of AMPK, PGC1α, UCP2, CPT1α, and Hadhb related to mitochondrial energy metabolism, which may be driven by increased Fiaf expression. These results firstly suggest that antimicrobial activities of RC and berberine may result in decreasing degradation of dietary polysaccharides, lowering potential calorie intake, and then systemically activating Fiaf protein and related gene expressions of mitochondrial energy metabolism in visceral adipose tissues. Taken together, these action mechanisms may contribute to significant anti-obesity effects. Findings in the present study also indicate that pharmacological regulation on gut microbes can develop an anti-obesity strategy.     

肠道微生物对肠道屏障功能完整性的维护机制研究概况

肠道微生物群是一个稳定且复杂的生态系统,可以通过形成菌膜屏障或促进肠道上皮细胞增殖分化等方式形成保护屏障,并在肠道病原菌感染和威胁期间维持和促进免疫稳态中起积极作用。本文重点叙述宿主-肠道微生物相互作用过程中抗病原菌感染的方式,以及肠道微生物参与合成抗菌化合物抵御肠道病原菌入侵和威胁的机制,为调控肠道微生物解决临床胃肠道疾病及其相关症状提供理论参考依据。     

Bacillus species in the intestine of termites and other soil invertebrates

Soil invertebrates harbour a complex microbial community in their intestinal system. The total number of microbes in the hindgut of soil invertebrates can reach a titre of 10(11) ml(-1). The gut microbes play an indispensable role in the digestion of food and are of ecological importance in the global carbon cycle. The gut microbiota can include a variety of micro-organisms from the three domains Bacteria, Archaea and Eucarya. The bacterial groups from the intestinal systems are mainly affiliated to the proteobacteria, the gram-positive groups Firmicutes and Actinobacteria, the Bacteroides/Flavobacterium branch and the spirochetes. The Archaea are represented by methanogens. The eukaryotic groups consist of protozoa, yeasts and fungi. Intestinal bacteria are involved in the degradation of cellulose, hemicellulose and aromatic compounds as well as nitrogen fixation. They also contribute to the redox status of the gut. Bacilli form a significant portion of the intestinal microbial community of soil invertebrates, especially among cellulose degraders. The diversity and function of bacilli in soil invertebrates will be discussed in this paper.     

瘤胃中木质纤维素降解菌及降解酶基因的研究进展

摘要：反刍动物瘤胃是公认的木质纤维素高效降解的天然反应器,对瘤胃微生物的研究成为开发生物能源的热点领域之一。其研究手段已经从传统的依赖分离培养从瘤胃中获得木质纤维素降解菌,并对降解菌中的木质纤维素降解酶逐一分析,发展到通过基因组/元基因组技术,直接从瘤胃中发现获得大量新的木质纤维素降解酶基因/基因簇,进而探讨其降解的分子机理。已有的研究结果表明,瘤胃微生物降解木质纤维素的过程非常复杂,其中涉及到大量不同种类的微生物、酶及基因/基因簇,随着新分析技术的建立和完善,对这些微生物、酶和基因的研究已取得了诸多进展。本论文综述报道了近期有关该方向的研究进展。     

Innate immune signalling at the intestinal epithelium in homeostasis and disease

The intestinal epithelium-which constitutes the interface between the enteric microbiota and host tissues-actively contributes to the maintenance of mucosal homeostasis and defends against pathogenic microbes. The recognition of conserved microbial products by cytosolic or transmembrane pattern recognition receptors in epithelial cells initiates signal transduction and influences effector cell function. However, the signalling pathways, effector molecules and regulatory mechanisms involved are not yet fully understood, and the functional outcome is poorly defined. This review analyses the complex and dynamic role of intestinal epithelial innate immune recognition and signalling, on the basis of results in intestinal epithelial cell-specific transgene or gene-deficient animals. This approach identifies specific epithelial cell functions within the diverse cellular composition of the mucosal tissue, in the presence of the complex and dynamic gut microbiota. These insights have thus provided a more comprehensive understanding of the role of the intestinal epithelium in innate immunity during homeostasis and disease.     

白蚁肠道微生物研究方法概述

白蚁是木质纤维素的主要降解者,在森林生态系统碳氮循环过程中发挥着重要作用。白蚁肠道共生微生物主要包括原生生物、细菌、古菌和真菌。在白蚁对木质纤维素进行降解、发酵,从而产生乙酸、氢气和甲烷以及对氮的固定过程中,白蚁肠道共生微生物起着重要的作用。本文对白蚁肠道微生物的研究方法进行总结,概述了各种方法的优缺点,同时对肠道微生物的研究进展进行了总结,以期为白蚁肠道微生物的进一步研究和利用提供参考。     

Gut microbes in cardiovascular diseases and their potential therapeutic applications

Microbial ecosystem comprises a complex community in which bacteria interact with each other.The potential roles of the intestinal microbiome play in human health have gained considerable attention.The imbalance of gut microbial community has been looked to multiple chronic diseases.Cardiovascular diseases(CVDs)are leading causes of morbidity worldwide and are influ-enced by genetic and environmental factors.Recent advances have provided scientific evidence that CVD may also be attributed to gut microbiome.in this review,we highlight the complex interplay between microbes,their metabolites,and the potential influence on the generation and development of CVDs.The therapeutic potentiai of using intestinal microbiomes to treat CVD is also discussed.it is quite possible that gut microbes may be used for clinical treatments of CVD in the near future.     

Sugar-induced conformational change found in the HA-33/HA-17 trimer of the botulinum toxin complex

Large-sized botulinum toxin complex (L-TC) is formed by conjugation of neurotoxin, nontoxic nonhemagglutinin and hemagglutinin (HA) complex. The HA complex is formed by association of three HA-70 molecules and three HA-33/HA-17 trimers, comprised of a single HA-17 and two HA-33 proteins. The HA-33/HA-17 trimer isolated from serotype D L-TC has the ability to bind to and penetrate through the intestinal epithelial cell monolayer in a sialic acid-dependent manner, and thus it plays an important role in toxin delivery through the intestinal cell wall. In this study, we determined the solution structure of the HA-33/HA-17 trimer by using small-angle X-ray scattering (SAXS). The SAXS image of HA-33/HA-17 exhibited broadly similar appearance to the crystal image of the complex. On the other hand, in the presence of N-acetylneuraminic acid, glucose and galactose, the solution structure of the HA-33/HA-17 trimer was drastically altered compared to the structure in the absence of the sugars. Sugar-induced structural change of the HA-33/HA-17 trimer may contribute to cell binding and subsequent transport across the intestinal cell layer.     

Anoxic Conditions Promote Species-Specific Mutualism between Gut Microbes In Silico

The human gut is inhabited by thousands of microbial species, most of which are still uncharacterized. Gut microbes have adapted to each other''s presence as well as to the host and engage in complex cross feeding. Constraint-based modeling has been successfully applied to predicting microbe-microbe interactions, such as commensalism, mutualism, and competition. Here, we apply a constraint-based approach to model pairwise interactions between 11 representative gut microbes. Microbe-microbe interactions were computationally modeled in conjunction with human small intestinal enterocytes, and the microbe pairs were subjected to three diets with various levels of carbohydrate, fat, and protein in normoxic or anoxic environments. Each microbe engaged in species-specific commensal, parasitic, mutualistic, or competitive interactions. For instance, Streptococcus thermophilus efficiently outcompeted microbes with which it was paired, in agreement with the domination of streptococci in the small intestinal microbiota. Under anoxic conditions, the probiotic organism Lactobacillus plantarum displayed mutualistic behavior toward six other species, which, surprisingly, were almost entirely abolished under normoxic conditions. This finding suggests that the anoxic conditions in the large intestine drive mutualistic cross feeding, leading to the evolvement of an ecosystem more complex than that of the small intestinal microbiota. Moreover, we predict that the presence of the small intestinal enterocyte induces competition over host-derived nutrients. The presented framework can readily be expanded to a larger gut microbial community. This modeling approach will be of great value for subsequent studies aiming to predict conditions favoring desirable microbes or suppressing pathogens.     

Modulation of the phagosome proteome by interferon-gamma

Macrophages are immune cells that function in the clearance of infectious particles. This process involves the engulfment of microbes into phagosomes where these particles are lysed and degraded. In the current study, we used a large scale quantitative proteomics approach to analyze the changes in protein abundance induced on phagosomes by interferon-gamma (IFN-gamma), an inflammatory cytokine that activates macrophages. Our analysis identified 167 IFN-gamma-modulated proteins on phagosomes of which more than 90% were up-regulated. The list of phagosomal proteins regulated by IFN-gamma includes proteins expected to alter phagosome maturation, enhance microbe degradation, trigger the macrophage immune response, and promote antigen loading on major histocompatibility complex (MHC) class I molecules. A dynamic analysis of IFN-gamma-sensitive proteins by Western blot indicated that newly formed phagosomes display a delayed proteolytic activity coupled to an increased recruitment of the MHC class I peptide-loading complex. These phagosomal conditions may favor antigen presentation by MHC class I molecules on IFN-gamma-activated macrophages.     

Influence of antibiotics on some intestinal microflora associated characteristics

Intestinal functions related to the presence of microbes in host organisms are normally heavily influenced by administration of antimicrobial drugs. We have investigated the effect of several antibiotics in man and rat, on some MACs (Microflora Associated Characteristics). A MAC is defined as the recording of any anatomical structure, biochemical or physiological function in the host organism which is influenced by microflora. When functional, active microbes are absent as in germfree animals, healthy newborns, or in relation to antimicrobial therapies, a MAC defined as a GAC (Germfree Animal Characteristic). Faecal samples have been collected prior to, during and up to several weeks after the antimicrobial administration in order to investigate different MAC/GAC patterns. Microbial conversion of cholesterol to coprostanol, bilirubin to urobilinogen and 7-alpha-dehydroxylation of cholic acid have been investigated to evaluate hepatic/intestinal co-functions, and degradation of intestinal mucin in order to evaluate the integrity in the intestinal mucosa. Furthermore, degradation of the dietary derived beta-aspartylglycine, the level of faecal trypsin and production of short chain fatty acids were investigated to evaluate dietary/intestinal co-functions. It is concluded that each antimicrobial drug creates its own profile, both with regard to duration and function.     

Microbes inside—from diversity to function: the case of Akkermansia

The human intestinal tract is colonized by a myriad of microbes that have developed intimate interactions with the host. In healthy individuals, this complex ecosystem remains stable and resilient to stressors. There is significant attention on the understanding of the composition and function of this intestinal microbiota in health and disease. Current developments in metaomics and systems biology approaches allow to probe the functional potential and activity of the intestinal microbiota. However, all these approaches inherently suffer from the fact that the information on macromolecules (DNA, RNA and protein) is collected at the ecosystem level. Similarly, all physiological and other information collected from isolated strains relates to pure cultures grown in vitro or in gnotobiotic systems. It is essential to integrate these two worlds of predominantly chemistry and biology by linking the molecules to the cells. Here, we will address the integration of omics- and culture-based approaches with the complexity of the human intestinal microbiota in mind and the mucus-degrading bacteria Akkermansia spp. as a paradigm.     

Biochemical analysis of starch degradation by Ruminobacter amylophilus 70.

Ruminobacter amylophilus is an obligate anaerobe that uses only alpha-linked glucose molecules (i.e., maltose, maltodextrins, and starch) as a source of energy, making it an excellent model for the study of bacterial starch degradation. Constitutive amylase, amylopectinase, and pullulanase activities were found in intracellular and extracellular fractions of R. amylophilus. However, extracellular activities apparently resulted from cell lysis. Both soluble and membrane-bound polysaccharidase activities were detected. Most of the soluble polysaccharidase activity partitioned with the periplasmic cell fraction. No alpha-glucosidase or maltase activity was detected in either the cellular or extracellular fraction. In addition, intact cells of R. amylophilus bound U-14C-starch. This binding could be saturated and was constitutive and sensitive to proteinase K, indicating protein or protein complex mediation. Competition experiments showed that these starch-binding sites had equally high affinities for starch and maltodextrins larger than maltotriose. The sites had a reduced affinity for maltose and virtually no affinities for glucose and nonstarch polysaccharides. These findings suggest that R. amylophilus binds starch molecules to the cell surface as an initial step in transporting the molecule through the outer membrane and into the periplasmic space. Extracellular polysaccharides do not appear to be involved in starch degradation.     

Small molecule activators of proteasome-related HslV peptidase

The HslVU is the proteasome-related two component system composed of HslV peptidase and HslU chaperone. It is involved in the degradation of an array of intracellular proteins. The presence of HslVU homologs in pathogenic microbes and its absence in human makes it an antimicrobial drug target. The functional HslVU complex forms when HslV dodecamer is flanked at both ends by HslU hexamers. In the HslVU complex, eight residues at the carboxy termini of HslU subunits intercalate into a clefts between two adjacent HslV subunits causing a conformational change in the active site of HslV which in turn results in the allosteric activation of HslV peptidase. Here, we report small molecules capable of activating HslV peptidase in the absence of its natural activator HslU ATPase. For this purpose, virtual screening of an in-house library of synthetic and natural compounds was performed to find out ligands mimicking the interaction of HslU carboxy terminus with HslV dodecamer. The benzimidazole, quinazoline and chromone derivatives were suggested by ligand docking to bind at the HslU carboxy termini intercalation pockets in the HslV dodecamer. This was confirmed by HslV activation and isothermal titration calorimetry assays with these compounds that gave ED₅₀ in sub-micromolar range (0.6–1.5 μM). The results showed for the first time that small, extracellular non-peptidic molecules can allosterically activate the peptide hydrolytic activity of HslV which in turn would initiate intracellular proteolysis.     

Microbial degradation of natural and of new synthetic polymers.

In landfills, deposited waste material is usually faced with strictly anoxic conditions. This means that the design of new biodegradable polymers must take into consideration that degradation should be possible especially in the absence of molecular oxygen. Poly-beta-hydroxybutyrate is depolymerized by the anaerobic fermenting bacterium Ilyobacter delafieldii through an extracellular hydrolase. Monomers are degraded inside the cells through classical beta-oxidation. Polyalkanoates containing odd-numbered or branched-chain acid monomers should he degraded in an analogous manner; in most cases the final mineralization of these residues requires special pathways. A comparison of the chemistry of natural polymer biodegradation leads to the conclusion that synthetic biodegradable polymers should be designed in the future to contain linkages which can be cleaved by extracellular hydrolytic enzymes. Recent findings on aerobic and anaerobic bacterial degradation of synthetic polyethers suggest that natural evolution of new depolymerizing enzymes, perhaps from existing hydrolases, could be possible in a reasonable amount of time, provided that the monomers are likely energy sources for a broad variety of microbes.     

白蚁-共生微生物系统降解木质纤维素研究进展

开发利用木质纤维素材料能显著增加地球上可再生资源的储备量。白蚁分布广泛,常见于热带和亚热带地区,它们借助细菌、古细菌、真菌等肠道微生物和原生动物协同降解食物中的木质纤维素,在生态系统的碳、氮循环中发挥着十分重要的作用。本文概括了近年来白蚁肠道微生物研究的进展,特别是近年来已被证明的肠道微生物在木质纤维素降解方面的作用,以期为后续研究木质纤维素的降解提供参考信息。     

Attenuated response of the serum triglyceride concentration to ingestion of a chocolate containing polydextrose and lactitol in place of sugar

We examined the effects of ingesting a non-sugar chocolate containing polydextrose and lactitol in place of sucrose and lactose on the concentrations of plasma glucose and serum insulin and triglyceride in humans. A regular chocolate was used as the control. A crossover study was employed, and the subjects each ingested 46 g of the control or non-sugar chocolate in the experiments. Alterations in the blood components were monitored for a period of 150 min after ingestion. The control chocolate elevated the concentrations of plasma glucose and serum insulin, with the peak occurring 30 min after ingestion, but the non-sugar chocolate had a very minor effect. The serum triglyceride concentration gradually increased after ingesting the control chocolate, but was only slightly elevated 150 min after ingesting the non-sugar chocolate. An animal study also showed an attenuated response of serum triglyceride to the administration of a fat emulsion containing polydextrose and lactitol, suggesting that the triglyceride transit through the gut was promoted by these compounds. These results suggest that, compared to regular chocolate, fat absorption in the gut was less after ingesting the non-sugar chocolate, presumably resulting in less effect on body fat deposition.     

Molecular Paths Linking Metabolic Diseases,Gut Microbiota Dysbiosis and Enterobacteria Infections

Alterations of both ecology and functions of gut microbiota are conspicuous traits of several inflammatory pathologies, notably metabolic diseases such as obesity and type 2 diabetes. Moreover, the proliferation of enterobacteria, subdominant members of the intestinal microbial ecosystem, has been shown to be favored by Western diet, the strongest inducer of both metabolic diseases and gut microbiota dysbiosis. The inner interdependence between the host and the gut microbiota is based on a plethora of molecular mechanisms by which host and intestinal microbes modify each other. Among these mechanisms are as follows: (i) the well-known metabolic impact of short chain fatty acids, produced by microbial fermentation of complex carbohydrates from plants; (ii) a mutual modulation of miRNAs expression, both on the eukaryotic (host) and prokaryotic (gut microbes) side; (iii) the production by enterobacteria of virulence factors such as the genotoxin colibactin, shown to alter the integrity of host genome and induce a senescence-like phenotype in vitro; (iv) the microbial excretion of outer-membrane vesicles, which, in addition to other functions, may act as a carrier for multiple molecules such as toxins to be delivered to target cells. In this review, I describe the major molecular mechanisms by which gut microbes exert their metabolic impact at a multi-organ level (the gut barrier being in the front line) and support the emerging triad of metabolic diseases, gut microbiota dysbiosis and enterobacteria infections.