Systematic analysis of gut bacterial carcinogen metabolism and its functional consequences

Organic carcinogens, in particular DNA-reactive compounds, contribute to the irreversible initiation step of tumorigenesis through introduction of genomic instability. Although carcinogen bioactivation and detoxification by human enzymes has been extensively studied, carcinogen biotransformation by human-associated bacteria, the microbiota, has not yet been systematically investigated. We tested the biotransformation of 68 mutagenic carcinogens by 34 bacterial species representative for the upper and lower human gastrointestinal tract and found that the majority (41) of the tested carcinogens undergo bacterial biotransformation. To assess the functional consequences of microbial carcinogen metabolism, we developed a pipeline to couple gut bacterial carcinogen biotransformation assays with Ames mutagenicity testing and liver biotransformation experiments. This revealed a bidirectional crosstalk between gut microbiota and host carcinogen metabolism, which we validated in gnotobiotic mouse models. Overall, the systematic assessment of gut microbiota carcinogen biotransformation and its interplay with host metabolism highlights the gut microbiome as an important modulator of exposome-induced tumorigenesis.