What has caused colorectal cancer? The answer to the question now seems more attainable due to the research led by two research teams of Professor Zhang Yan and Professor Yuchi Zhiguang from Tianjin University and collaboration teams at UIUC and A*Star led by Professor Zhao Huimin and Professor Ee Lui Ang. Together, they have discovered the mechanism by which bacteria living in the human gut convert taurine into hydrogen sulfide, a gaseous compound associated with the odor of rotten eggs and farts. Their research is reported in the journal “Nature Communications”. Taurine is present in certain food products and is a component of bile. Its abundance is correlated with a diet rich in meat and fat. Taurine is a major source of sulfur in the human gut, and it is metabolized by certain gut bacteria into toxic hydrogen sulfide, which can lead to serious effects, such as inflammation and colorectal cancer.

The carbon-sulfur bond in taurine is extremely strong, and cleavage of taurine to release the sulfur atom generally requires harsh reaction conditions and molecular oxygen. In this study, researchers have found that certain gut bacteria, which live in the absence of oxygen, can carry out taurine cleavage using a new chemical mechanism involving free radicals. This mechanism explains the decades-old mystery of how anaerobic bacteria are able to metabolize taurine and related sulfur-containing molecules in the absence of oxygen.

Gut bacteria produce both harmful and beneficial compounds, and exert profound effects on human health. However, the diverse metabolic reactions carried out by gut bacteria are still poorly understood. The researchers hope that the current findings will add to our understanding of sulfur chemistry in the human gut, and lead to future treatments for diseases and dietary guidelines for human health.