The human intestinal system contains a complex community of microorganisms, the intestinal microbiome, which metabolizes food components that have not readily been digested. However, there are also microbial degradation processes occurring in the colon that may have negative effects on the human host. A research team headed by biologist Dr. David Schleheck reports that a key enzyme was discovered in a research collaboration with Harvard University (U.S.). This enzyme is involved in the degradation of the substrate taurine, which is abundant in the colon, by the intestinal bacterium Bilophila wadsworthia. This process generates toxic hydrogen sulphide. Increased hydrogen sulphide production is thought to be associated with higher permeability of the intestinal barrier, and higher susceptibility to infections and colon cancer. Moreover, Bilophila wadsworthia can act as a pathogen, for example, in appendicitis. The results were published in the current issue of the Proceedings of the National Academy of Sciences (PNAS).