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Theses

Métabolisme des flavan-3-ols par le microbiote intestinal humain : mise en évidence d’espèces bactériennes et de gènes impliqués dans la fonction

Abstract : Flavan-3-ols are among the most consumed polyphenols by humans and are present as monomers and oligomers such as procyanidins. The majority of flavan-3-ols reach the colon where the intestinal microbiota resides. While the metabolic pathways for the degradation of flavan-3-ols by the microbiota are relatively well described, only a few microorganisms and microbial genes involved in these pathways are known. The objective of the thesis was therefore to identify the microorganisms and genes involved in the degradation of flavan-3-ols and in particular procyanidins. From human stools of three healthy individuals, culturomic approaches combined with screening for the metabolic activity of bacterial isolates by HPLC-DAD allowed us to obtain four strains of the species Eggerthella lenta and one strain of the species Flavonifractor plautii degrading (+)-catechin and (-)-epicatechin. The activity of these strains was then tested on B-type (DP2 to 4) and A-type (DP2) procyanidins and the metabolites generated were characterized by LC-ESI-MS / MS. We have thus shown for the first time that E. lenta degrades procyanidins. The reaction catalyzed by E. lenta on dimers (B-type and A type), corresponds to the opening of the C-ring of the terminal unit. By a transcriptomic approach (RNAseq) carried out in E. lenta, coupled with the heterologous expression of the genes of interest in Escherichia coli, we have discovered two genes (fmber1, fmber2) encoding two benzyl ether reductases involved in the opening of the C ring of the monomers and an operon of two genes (pber) catalyzing this reaction on the dimers of type-B procyanidins. Finally, two operons of three genes (cadh, ecadh) encoding two enzymatic complexes involved in the dehydroxylation of the B-ring of (+)-catechin and (-)-epicatechin have also been identified. In conclusion, the species E. lenta and F. plautii, as well as the genes identified in this study, will constitute good markers of the microbial metabolism of flavan-3-ols in humans in the future. This will ultimately allow a better understanding of the effects of the consumption of flavan-3-ols in individuals in good health or at risk of chronic diseases.
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https://hal.inrae.fr/tel-03249354
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Submitted on : Friday, June 4, 2021 - 9:57:56 AM
Last modification on : Saturday, June 5, 2021 - 3:41:12 AM

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  • HAL Id : tel-03249354, version 1

Citation

Ruben Halifa. Métabolisme des flavan-3-ols par le microbiote intestinal humain : mise en évidence d’espèces bactériennes et de gènes impliqués dans la fonction. Sciences du Vivant [q-bio]. ÉCOLE DOCTORALE DES SCIENCES DE LA VIE, SANTÉ, AGRONOMIE, ENVIRONNEMENT, 2021. Français. ⟨tel-03249354⟩

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