@article{BrauneMaulSchebbetal.2010,
  author    = {Braune, Annett and Maul, Ronald and Schebb, Nils Helge and Kulling, Sabine E. and Blaut, Michael},
  title     = {The red clover isoflavone irilone is largely resistant to degradation by the human gut microbiota},
  issn      = {1613-4125},
  doi       = {10.1002/mnfr.200900233},
  year      = {2010},
  abstract  = {Intestinal bacteria may influence bioavailability and physiological activity of dietary isoflavones. We therefore investigated the ability of human intestinal microbiota to convert irilone and genistein in vitro. In contrast to genistein, irilone was largely resistant to transformation by fecal slurries of ten human subjects. The fecal microbiota converted genistein to dihydrogenistein, 6'-hydroxy-O-desmethylangolensin, and 2-(4-hydroxyphenyl)- propionic acid. However, considerable interindividual differences in the rate of genistein degradation and the pattern of metabolites formed from genistein were observed. Only one metabolite, namely dihydroirilone, was formed from irilone in minor amounts. In further experiments, Eubacterium ramulus, a prevalent flavonoid-degrading species of the human gut, was tested for transformation of irilone. In contrast to genistein, irilone was not converted by E. ramulus. Irilone only differs from genistein by a methylenedioxy group attached to the A-ring of the isoflavone skeleton. This substitution obviously restricts the degradability of irilone by human intestinal bacteria.},
  language  = {en}
}
@article{BrauneGuetschowBlaut2019,
  author    = {Braune, Annett and G{\"u}tschow, Michael and Blaut, Michael},
  title     = {An NADH-Dependent Reductase from Eubacterium ramulus Catalyzes the Stereospecific Heteroring Cleavage of Flavanones and Flavanonols},
  series = {Applied and environmental microbiology},
  volume    = {85},
  journal   = {Applied and environmental microbiology},
  number    = {19},
  publisher = {American Society for Microbiology},
  address   = {Washington},
  issn      = {0099-2240},
  doi       = {10.1128/AEM.01233-19},
  pages     = {15},
  year      = {2019},
  abstract  = {The human intestinal anaerobe Eubacterium ramulus is known for its ability to degrade various dietary flavonoids. In the present study, we demonstrate the cleavage of the heterocyclic C-ring of flavanones and flavanonols by an oxygen-sensitive NADH-dependent reductase, previously described as enoate reductase, from E. ramulus. This flavanone- and flavanonol-cleaving reductase (Fcr) was purified following its heterologous expression in Escherichia coli and further characterized. Fcr cleaved the flavanones naringenin, eriodictyol, liquiritigenin, and homoeriodictyol. Moreover, the flavanonols taxifolin and dihydrokaempferol served as substrates. The catalyzed reactions were stereospecific for the (2R)-enantiomers of the flavanone substrates and for the (25,35)-configured flavanonols. The enantioenrichment of the nonconverted stereoisomers allowed for the determination of hitherto unknown flavanone racemization rates. Fcr formed the corresponding dihydrochalcones and hydroxydihydrochalcones in the course of an unusual reductive cleavage of cyclic ether bonds. Fcr did not convert members of other flavonoid subclasses, including flavones, flavonols, and chalcones, the latter indicating that the reaction does not involve a chalcone intermediate. This view is strongly supported by the observed enantiospecificity of Fcr. Cinnamic acids, which are typical substrates of bacterial enoate reductases, were also not reduced by Fcr. Based on the presence of binding motifs for dinucleotide cofactors and a 4Fe-4S cluster in the amino acid sequence of Fcr, a cofactor-mediated hydride transfer from NADH onto C-2 of the respective substrate is proposed. IMPORTANCE Gut bacteria play a crucial role in the metabolism of dietary flavonoids, thereby contributing to their activation or inactivation after ingestion by the human host. Thus, bacterial activities in the intestine may influence the beneficial health effects of these polyphenolic plant compounds. While an increasing number of flavonoid-converting gut bacterial species have been identified, knowledge of the responsible enzymes is still limited. Here, we characterized Fcr as a key enzyme involved in the conversion of flavonoids of several subclasses by Eubacterium ramulus, a prevalent human gut bacterium. Sequence similarity of this enzyme to hypothetical proteins from other flavonoid-degrading intestinal bacteria in databases suggests a more widespread occurrence of this enzyme. Functional characterization of gene products of human intestinal microbiota enables the assignment of metagenomic sequences to specific bacteria and, more importantly, to certain activities, which is a prerequisite for targeted modulation of gut microbial functionality.},
  language  = {en}
}
@article{BurkhardtRauschKlopfleischetal.2021,
  author    = {Burkhardt, Wiebke and Rausch, Theresa and Klopfleisch, Robert and Blaut, Michael and Braune, Annett},
  title     = {Impact of dietary sulfolipid-derived sulfoquinovose on gut microbiota composition and inflammatory status of colitis-prone interleukin-10-deficient mice},
  series = {International journal of medical microbiology : IJMM},
  volume    = {311},
  journal   = {International journal of medical microbiology : IJMM},
  number    = {3},
  publisher = {Elsevier},
  address   = {M{\"u}nchen},
  issn      = {1618-0607},
  doi       = {10.1016/j.ijmm.2021.151494},
  pages     = {11},
  year      = {2021},
  abstract  = {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.},
  language  = {en}
}