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

Abstract

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.

Keywords: anaerobic metabolism; flavonoid; gut bacteria; intestinal microbiota; polyphenol.

Figure 1.

Basic flavan structure and flavonoid classes discussed in more detail in this review.

Figure 2.

Pathways of the conversion of (A) flavonols using the example of quercetin and (B) flavones using the example of apigenin by human intestinal bacteria.

Figure 3.

Pathways of the conversion of isoflavones using the examples of daidzein and genistein by human intestinal bacteria. The dashed arrow indicates a controversially discussed reaction.

Figure 4.

Pathway of the conversion of flavan-3-ols using the example of (epi)catechin.