Résumé
Introduction: Accumulating evidence is supporting the protective effect of whole grains against several chronic diseases. Simultaneously, our knowledge is increasing on the impact of gut microbiota on our health and how diet can modify the composition of our bacterial cohabitants. Aim: We aimed to determine the effect of bran-enriched diets on the gut microbial composition and to assess the potential contribution of gut microbiota to the metabolism of betaine. According to our hypothesis, some of the betainized compounds previously detected from various tissues may be produced by microbiota.Materials and methods: We studied C57BL/6J mice fed with diets enriched with rye bran and wheat aleurone, conventional and germ-free C57BL/6NTac mice on a basal diet, and the colonic fermentation of rye bran in an in vitro model of the human gastrointestinal system. We performed 16S rRNA gene sequencing and metabolomics on the study samples to determine the correlations between bacterial and metabolite abundance.Results and discussion: The bran-enriched diets elevated the levels of betainized compounds in the colon contents of C57BL/6J mice and increased the abundance of several bacterial taxa, including Akkermansia, Bifidobacterium, Coriobacteriaceae, Lactobacillus, Parasutterella, and Ruminococcus. Many of these bacteria are associated with improved health status or the metabolism of plant-based molecules. The levels of betainized compounds in the gut tissues of germ-free mice were significantly lower compared to conventional mice. In the in vitro model of the human gut, the production of betainized compounds was observed throughout the incubation, while the levels of glycine betaine decreased. Our findings suggest that gut microbes affected by the bran-based diet are also involved in the metabolism of glycine betaine into other betainized compounds, adding another potential compound group acting as a mediator of the synergistic metabolic effect of diet and colonic microbiota.