Explore the vast range of titles available.

Degradation of complex dietary fiber by gut microbes is essential for colonic fermentation, short-chain fatty acid production, and microbiome function. Ruminococcus bromii is the primary resistant starch (RS) degrader in humans, which relies on the amylosome, a specialized cell-bound enzymatic complex. To unravel its architecture, function, and the interplay among its components, we applied a holistic multilayered approach: Cryo-electron tomography reveals that the amylosome comprises a constitutive extracellular layer extending toward the RS substrate. Proteomics demonstrates remodeling of its contents across different growth conditions, with Amy4 and Amy16 comprising 60% of the amylosome in response to RS. Structural and biochemical analyses reveal complementarity and synergistic RS degradation by these enzymes. We demonstrate that amylosome composition and RS degradation are regulated at two levels: structural constraints and expression-driven shifts in enzyme proportions enforce enzyme proximity, which allows R. bromii to fine-tune its adaptation to dietary fiber and shape colonic metabolism. Here, combining structural, proteomics and biochemical analyses, the authors elucidate how the keystone gut bacterium Ruminococcus bromii assembles a specialized enzyme complex, the amylosome, to efficiently break down resistant starch, a cardinal dietary fiber that influences gut microbiome function and health.

A decrease in the abundance and biodiversity of intestinal bacteria within the Firmicutes phylum has been associated with inflammatory bowel disease (IBD). In particular, the anti-inflammatory bacterium Faecalibacterium prausnitzii, member of the Firmicutes phylum and one of the most abundant species in healthy human colon, is underrepresented in the microbiota of IBD patients. The aim of this study was to investigate the immunomodulatory properties of F. prausnitzii strain A2-165, the biofilm forming strain HTF-F and the extracellular polymeric matrix (EPM) isolated from strain HTF-F. For this purpose, the immunomodulatory properties of the F. prausnitzii strains and the EPM were studied in vitro using human monocyte-derived dendritic cells. Then, the capacity of the F. prausnitzii strains and the EPM of HTF-F to suppress inflammation was assessed in vivo in the mouse dextran sodium sulphate (DSS) colitis model. The F. prausnitzii strains and the EPM had anti-inflammatory effects on the clinical parameters measured in the DSS model but with different efficacy. The immunomodulatory effects of the EPM were mediated through the TLR2-dependent modulation of IL-12 and IL-10 cytokine production in antigen presenting cells, suggesting that it contributes to the anti-inflammatory potency of F. prausnitzii HTF-F. The results show that F. prausnitzii HTF-F and its EPM may have a therapeutic use in IBD.

Active inflammatory bowel disease (IBD) often coincides with increases of Ruminococcus gnavus, a gut microbe found in nearly everyone. It was not known how, or if, this correlation contributed to disease. We investigated clinical isolates of R. gnavus to identify molecular mechanisms that would link R. gnavus to inflammation. Here, we show that only some isolates of R. gnavus produce a capsular polysaccharide that promotes a tolerogenic immune response, whereas isolates lacking functional capsule biosynthetic genes elicit robust proinflammatory responses in vitro. Germ-free mice colonized with an isolate of R. gnavus lacking a capsule show increased measures of gut inflammation compared to those colonized with an encapsulated isolate in vivo. These observations in the context of our earlier identification of an inflammatory cell-wall polysaccharide reveal how some strains of R. gnavus could drive the inflammatory responses that characterize IBD.

Background: The intestinal mucus layer plays a key role in the maintenance of host-microbiota homeostasis. To document the crosstalk between the host and microbiota, we used gnotobiotic models to study the influence of two major commensal bacteria, Bacteroides thetaiotaomicron and Faecalibacterium prausnitzii, on this intestinal mucus layer. B. thetaiotaomicron is known to use polysaccharides from mucus, but its effect on goblet cells has not been addressed so far. F. prausnitzii is of particular physiological importance because it can be considered as a sensor and a marker of human health. We determined whether B. thetaiotaomicron affected goblet cell differentiation, mucin synthesis and glycosylation in the colonic epithelium. We then investigated how F. prausnitzii influenced the colonic epithelial responses to B. thetaiotaomicron.[br/] Results: B. thetaiotaomicron, an acetate producer, increased goblet cell differentiation, expression of mucus-related genes and the ratio of sialylated to sulfated mucins in mono-associated rats. B. thetaiotaomicron, therefore, stimulates the secretory lineage, favoring mucus production. When B. thetaiotaomicron was associated with F. prausnitzii, an acetate consumer and a butyrate producer, the effects on goblet cells and mucin glycosylation were diminished. F. prausnitzii, by attenuating the effects of B. thetaiotaomicron on mucus, may help the epithelium to maintain appropriate proportions of different cell types of the secretory lineage. Using a mucus-producing cell line, we showed that acetate up-regulated KLF4, a transcription factor involved in goblet cell differentiation.[br/] Conclusions: B. thetaiotaomicron and F. prausnitzii, which are metabolically complementary, modulate, in vivo, the intestinal mucus barrier by modifying goblet cells and mucin glycosylation. Our study reveals the importance of the balance between two main commensal bacteria in maintaining colonic epithelial homeostasis via their respective effects on mucus.

One of the main mechanisms of nanoparticle toxicity is known to be the generation of reactive oxygen species (ROS) which primarily damage cell membranes. However, very limited data on membrane effects in anaerobic environments (where ROS could not be the cause of membrane damage) are available. In the following study, rumen anaerobe Ruminococcus flavefaciens 007C was used as a bacterial model to assess the potential effects of Al 2 O 3 and TiO 2 nanoparticles on membranes in an anaerobic environment. Fatty acid profiles of cultures after exposure to Al 2 O 3 or TiO 2 nanoparticles were analyzed and compared with the profiles of non-exposed cultures or cultures exposed to bulk materials. Analysis revealed dose–effect changes in membrane composition exclusively when cells were exposed to Al 2 O 3 nanoparticles in a concentration range of 3–5 g/L, but were not present in cultures exposed to bulk material. On the other hand, the tested concentrations of nano-TiO 2 did not significantly affect the membrane profile of the exposed bacterium. The results suggest the possibility that Al 2 O 3 induces changes in bacterial membranes by direct physical interaction, which was supported by TEM image analysis.

Abstract Hydrolysis of cellulose requires two different types of cellulases: exo- and endocellulase. Here, we investigated for the hydrolysis of cellulose by two types of cellulases, an endoglucanase (Cel5) from Ruminococcus albus fused with the xylanase A cellulose binding domain II (CBM6) of Clostridium stercorarium and Thermobifidus fusca E3, an exoglucanase (Cel6B). Cel5-CBM6 or Cel6B showed a linear relationship between the production of soluble sugars and the incubation time when native alfalfa cellulose was used as a substrate. Cel5-CBM6 produces more soluble sugars than Cel6B and the hydrolysis of cellulose by a mixture of the two enzymes produces substantially more (22%) soluble sugars than the total amount produced by these enzymes individually. Although Cel5-CBM6 solubilized high quantities of sugars from alfalfa cellulose, it did not significantly decrease its crystallinity, while Cel6B decreased the crystallinity of cellulose by 34%. When the two cellulases were combined, a decrease of more than 50% in the content of crystalline cellulose was observed. The enzyme–gold labeling experiments revealed that both enzymes showed a high affinity for all substrates. Furthermore, simultaneous visualization of the enzyme-binding sites revealed the preferred substrates in native lignocellulosic material. When plant cellulose was pre-incubated with Cel5-CBM6, density of the gold labeling greatly increased suggesting that preliminary exposure of lignocellulosic material to Cel5-CBM6 may have enhanced the accessibility of the substrate to Cel5-CBM6 and Cel6B. This result provides a plausible explanation for the observed endo/exo cellulase synergism during hydrolysis.

An obligatory step in cellulose degradation by anaerobic bacteria is the adhesion of the bacterium to the polysaccharide. In many anaerobic bacteria the adhesion protein, and the enzymes required for extensive polysaccharide hydrolysis, are organized into a complex and interesting structure called the cellulosome. The Gram-positive anaerobe Ruminococcus albus also produces a cellulosome-like complex, but the bacterium appears to possess other mechanism(s) for adhesion to plant surfaces and genes encoding functions relevant to growth on cellulose are conditionally expressed, as suggested by a combination of functional proteomics, differential display reverse-transcriptase PCR, and mutational analysis. A novel form of cellulose-binding protein has been identified and shown to belong to the Pil-protein family, being most similar to the type 4 fimbrial proteins of Gram-negative, pathogenic bacteria. These studies have provided new insights into the adhesion of bacteria to plant surfaces, and call attention to the likely existence of genetically analogous adhesion determinants in both pathogenic and non-pathogenic bacteria.