Despite identifying urobilin as the yellow pigment in urine more than 125 years ago, the enzyme responsible for its production has remained a mystery. Now, NLM Intramural Research Program investigator Xiaofang Jiang, PhD, and her team have identified the microbial enzyme responsible for giving urine its yellow hue. The results found that this enzyme is almost always present in the guts of healthy adults but is often missing in young infants and adults with Inflammatory Bowel Disease. These findings have the potential to guide future work related to developing new probiotic therapies that could lead to clinical improvements and outcomes for patients. Their paper, “Discovery of a gut microbial enzyme that reduces bilirubin to urobilinogen,” was published in the journal Nature Microbiology.