Impact of dietary sulfolipid-derived sulfoquinovose on gut microbiota composition and inflammatory status of colitis-prone interleukin-10-deficient mice

The interplay between diet, intestinal microbiota and host is a major factor impacting health. A diet rich in unsaturated fatty acids has been reported to stimulate the growth of Bilophila wadsworthia by increasing the proportion of the sulfonated bile acid taurocholate (TC). The taurine-induced overgrowth of B. wadsworthia promoted the development of colitis in interleukin-10-deficient (IL-10-/-) mice. This study aimed to investigate whether intake of the sulfonates sulfoquinovosyl diacylglycerols (SQDG) with a dietary supplement or their degradation product sulfoquinovose (SQ), stimulate the growth of B. wadsworthia in a similar manner and, thereby, cause intestinal inflammation. Conventional IL-10-/- mice were fed a diet supplemented with the SQDG-rich cyanobacterium Arthrospira platensis (Spirulina). SQ or TC were orally applied to conventional IL-10-/- mice and gnotobiotic IL-10-/- mice harboring a simplified human intestinal microbiota with or without B. wadsworthia. Analyses of inflammatory parameters revealed that none of the sulfonates induced severe colitis, but both, Spirulina and TC, induced expression of pro-inflammatory cytokines in cecal mucosa. Cell numbers of B. wadsworthia decreased almost two orders of magnitude by Spirulina feeding but slightly increased in gnotobiotic SQ and conventional TC mice. Changes in microbiota composition were observed in feces as a result of Spirulina or TC feeding in conventional mice. In conclusion, the dietary sulfonates SQDG and their metabolite SQ did not elicit bacteria-induced intestinal inflammation in IL-10-/- mice and, thus, do not promote colitis

Bacterial species involved in the conversion of dietary flavonoids in the human gut

The gut microbiota plays a crucial role in the conversion of dietary flavonoids and thereby affects their health-promoting effects in the human host. The identification of the bacteria involved in intestinal flavonoid conversion has gained increasing interest. This review summarizes available information on the so far identified human intestinal flavonoid-converting bacterial species and strains as well as their enzymes catalyzing the underlying reactions. The majority of described species involved in flavonoid transformation are capable of carrying out the O-deglycosylation of flavonoids. Other bacteria cleave the less common flavonoid-C-glucosides and/or further degrade the aglycones of flavonols, flavanonols, flavones, flavanones, dihydrochalcones, isoflavones and monomeric flavan-3-ols. To increase the currently limited knowledge in this field, identification of flavonoid-converting bacteria should be continued using culture-dependent screening or isolation procedures and molecular approaches based on sequence information of the involved enzymes

Isolation of a Human Intestinal Bacterium Capable of Daidzein and Genistein Conversion▿

A rod-shaped gram-positive anaerobic bacterium, strain HE8, was isolated from human feces. The isolate was able to convert the isoflavones daidzein and genistein to equol and 5-hydroxy-equol, respectively. Based on phenotypic and phylogenetic analyses, strain HE8 is described as a new species, Slackia isoflavoniconvertens

Flavonoid-Modifying Capabilities of the Human Gut Microbiome—An In Silico Study

Flavonoids are a major group of dietary plant polyphenols and have a positive health impact, but their modification and degradation in the human gut is still widely unknown. Due to the rise of metagenome data of the human gut microbiome and the assembly of hundreds of thousands of bacterial metagenome-assembled genomes (MAGs), large-scale screening for potential flavonoid-modifying enzymes of human gut bacteria is now feasible. With sequences of characterized flavonoid-transforming enzymes as queries, the Unified Human Gastrointestinal Protein catalog was analyzed and genes encoding putative flavonoid-modifying enzymes were quantified. The results revealed that flavonoid-modifying enzymes are often encoded in gut bacteria hitherto not considered to modify flavonoids. The enzymes for the physiologically important daidzein-to-equol conversion, well studied in Slackiaisoflavoniconvertens, were encoded only to a minor extent in Slackia MAGs, but were more abundant in Adlercreutzia equolifaciens and an uncharacterized Eggerthellaceae species. In addition, enzymes with a sequence identity of about 35% were encoded in highly abundant MAGs of uncultivated Collinsella species, which suggests a hitherto uncharacterized daidzein-to-equol potential in these bacteria. Of all potential flavonoid modification steps, O-deglycosylation (including derhamnosylation) was by far the most abundant in this analysis. In contrast, enzymes putatively involved in C-deglycosylation were detected less often in human gut bacteria and mainly found in Agathobacter faecis (formerly Roseburia faecis). Homologs to phloretin hydrolase, flavanonol/flavanone-cleaving reductase and flavone reductase were of intermediate abundance (several hundred MAGs) and mainly prevalent in Flavonifractor plautii. This first comprehensive insight into the black box of flavonoid modification in the human gut highlights many hitherto overlooked and uncultured bacterial genera and species as potential key organisms in flavonoid modification. This could lead to a significant contribution to future biochemical-microbiological investigations on gut bacterial flavonoid transformation. In addition, our results are important for individual nutritional recommendations and for biotechnological applications that rely on novel enzymes catalyzing potentially useful flavonoid modification reactions

Short- and Branched-Chain Fatty Acids as Fecal Markers for Microbiota Activity in Vegans and Omnivores

A vegan diet could impact microbiota composition and bacterial metabolites like short-chain (SCFA) and branched-chain fatty acids (BCFA). The aim of this study was to compare the concentrations of SCFA, BCFA, ammonia, and fecal pH between vegans and omnivores. In this cross-sectional study (vegans n = 36; omnivores n = 36), microbiota composition, fecal SCFA, BCFA, and ammonia concentrations and pH were analyzed in complete stool samples. A random forest regression (RFR) was used to identify bacteria predicting SCFA/BCFA concentrations in vegans and omnivores. No significant differences in SCFA and BCFA concentrations were observed between vegans and omnivores. Fecal pH (p = 0.005) and ammonia concentration (p = 0.01) were significantly lower in vegans than in omnivores, while fiber intake was higher (p < 0.0001). Shannon diversity was higher in omnivores compared to vegans on species level (p = 0.04) only. In vegans, a cluster of Faecalibacterium prausnitzii, Prevotella copri, Dialister spp., and Eubacterium spp. was predictive for SCFA and BCFA concentrations. In omnivores, Bacteroides spp., Clostridium spp., Ruminococcus spp., and Prevotella copri were predictive. Though SCFA and BCFA did not differ between vegans and omnivores, the results of the RFR suggest that bacterial functionality may be adapted to varying nutrient availability in these diets

The F₄₂₀H₂-dehydrogenase from Methanolobus Tindarius: Cloning of the Ffd Operon and Expression of the Genes in Escherichia Coli

The membrane-bound F420H2-dehydrogenase from the methylotrophic methanogen Methanolobus tindarius oxidizes reduced coenzyme F420 and feeds the electrons into an energy-conserving electron transport chain. Based on the N-terminal amino acid sequence of the 40-kDa subunit of F420H2-dehydrogenase the corresponding gene ffdB was detected in chromosomal DNA of M. tindarius. Sequence analysis, primer extension, and RT-PCR experiments indicated that ffdB is part of an operon harboring three additional open reading frames (ffdA, ffdC, ffdD). The corresponding mRNA transcript and transcription start sites were determined. All four genes could be heterologously expressed in Escherichia coli