The strict anaerobic gut microbe Eubacterium hallii transforms the carcinogenic dietary heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP).

2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) is the most abundant food-derived heterocyclic aromatic amine in well-cooked meats and may contribute to the recognized carcinogenicity of processed meats. In this study, a panel of human gut microbes was tested for their ability to convert PhIP to a conjugate PhIP-M1. Eubacterium hallii was newly identified to catalyse the conversion of PhIP to PhIP-M1 with high efficiency. The reaction was shown to involve the metabolism of glycerol to 3-hydroxypropionaldehyde as a key pathway. The proficiency of E. hallii in transforming PhIP in the presence of a complex intestinal microbiota was confirmed using batch fermentations inoculated with effluents from a continuous intestinal fermentation model mimicking human proximal and distal colon microbiota. In batch fermentations inoculated with proximal colon microbiota, PhIP-M1 transformation corresponded to an up to 300-fold increase of E. hallii. In contrast, PhIP transformation of distal colon microbiota was low but increased by 120-fold after supplementation with E. hallii. These findings indicate for the first time the relevance of the abundant commensal strict anaerobe E. hallii in the transformation of a dietary carcinogen that could contribute to its detoxification in the human colon.