Bioactivation of polyphenolic plant compounds by human gut bacteria

Project Leader: Dr. Annett Braune
Team: Dr. Tobias Goris, Anke Gühler, Sabine Schmidt

Lichtmikroskopische Aufnahme des humanen Darmbakteriums Catenibacillus scindens
Fig. 1 The human intestinal bacterium Catenibacillus scindens was newly isolated and described in detail. It is capable of cleaving C- and O-coupled polyphenolic glucosides. Light micrograph following Gram staining. (© DIfE)

Polyphenols are a major class of secondary plant compounds present in plant-based foods, beverages and dietary supplements. Epidemiological, preclinical and clinical studies increasingly support a role of polyphenolic compounds in the prevention of various disorders including cardiovascular disease, type 2 diabetes, obesity and cancer.

However, the majority of ingested polyphenols are poorly absorbed in the small intestine or return to the gut via enterohepatic circulation following their absorption. As a result, substantial quantities of these compounds reach the colon, where bacterial density is high. In the colon polyphenols may affect the composition of the resident microbial community by inhibiting or promoting the growth of certain bacterial species or they may undergo conversion by intestinal bacteria, which may lead to their bioactivation. In this way, bacterial species may contribute to the proposed preventive effects of dietary polyphenols. Knowledge on the bacteria responsible for polyphenol conversion and their corresponding enzymes is still limited even though these bacterial activities contribute to different polyphenol-metabolizing phenotypes of the human host.

Therefore, we identify polyphenol-converting gut bacteria and also isolate novel bacterial strains involved in the transformation of polyphenols (Fig. 1). We strive to unravel the pathways underlying the conversion of relevant polyphenols including the characterization of the involved enzymes. The knowledge gained by these investigations will clarify, which bacterial species are responsible for the bioactivation of ingested polyphenols in humans and how these bacteria contribute to the observed inter-individual differences in the conversion of these health-relevant plant compounds.

As part of the EU joint research project SynBio4Flav (Synthetic Biology for the Production of Flavonoids) we are involved with the biotechnological production of bioactive flavonoids. Flavonoids represent a large group of polyphenols. At DIfE, we focus on flavonoid-modifying enzymes from bacteria present in the human gut. These novel enzymes will be employed as variable modules in synthetic biochemical pathways for production of high-value flavonoids by microbial consortia.