Metabolization of Flavan-3-ol Oligomers by Eggerthella lenta, a Human Gut Bacterium

Flavan-3-ols are among the most widely consumed flavonoids and have been implicated in the prevention of cardiometabolic diseases. Increasing evidence indicates that phenolic metabolites produced by the gut microbiota from flavan-3-ols contribute significantly to these effects. While some bacterial species can metabolize flavan-3-ol monomers, no isolates with activity on oligomers, i.e., procyanidins, have been reported. Since the gut microbiota is known to hydrolyze procyanidins, our aim was to identify bacteria capable of degrading them and to characterize their resulting metabolites. Through culturomic, genomic, and metabolomic approaches, we isolated novel strains of Eggerthella lenta and Flavonifractor plautii that metabolize flavan-3-ol monomers. Their activity was subsequently tested on B-type (DP 2 to 4) and A-type (DP 2) procyanidins. Only E. lenta was able to convert procyanidins, whereas F. plautii, either alone or in co-culture with E. lenta, showed no detectable activity. The reaction catalyzed by E. lenta corresponded to C-ring opening of the terminal unit of the oligomers. This work provides the first demonstration of procyanidin metabolism by a human gut bacterium. The presence and activity of E. lenta in the gut may therefore be a key determinant of the health benefits associated with flavan-3-ol-rich diets.