Scientists say they have finally answered the age-old question: “Why is our pee yellow?” In a new study, researchers discovered that enzymes produced by gut bacteria play a key role in mellowing urine. Curiosity aside, this discovery may actually help scientists better understand the gut microbiome and how it contributes to certain health conditions, such as jaundice in newborns.
Urine is the final stage of our body natural drainage system. It is made from excess water and waste products filtered from the blood through the kidneys. Some of these waste products are produced when our cells reach the end of their life cycle, such as red blood cells, which use hemoglobin to carry oxygen throughout the body. An important compound produced by red blood cells is heme, the precursor of hemoglobin, and the eventual breakdown of red blood cells and their heme causes a series of events that cause urine to turn yellow.
Scientists have long known that a chemical called urobilin is the main cause of the yellow color in urine. However, according to lead author Brantley Hall, an assistant professor in the Department of Cell Biology and Molecular Genetics at the University of Maryland, we do not know about the key step that leads to the presence of urobilin in urine: the role played by gut bacteria. is still in the dark. further breaks down heme byproducts.
in research published Hall and his team detailed the missing piece of the puzzle Wednesday in the journal Nature Microbiology.
“When red blood cells break down over their six-month lifespan, a bright orange pigment called bilirubin is produced as a byproduct. Once in the intestine, resident bacteria convert bilirubin into molecules that turn yellow when exposed to oxygen. “This molecule, urobilin, is the main cause of yellow urine,” Hall told Gizmodo in an email. “In this research, we discovered the enzyme responsible for this reaction.”
The research team devised a newly discovered enzyme, bilirubin reductase (BilR). They discovered the gene responsible for the production of this enzyme in certain enteric bacteria in the large intestine, in particular a group of bacteria called Firmicutes, and were able to confirm its function in the breakdown of bilirubin (more specifically Specifically, BilR converts bilirubin to urobilinogen (which then turns to urobilin in the presence of air). They also showed that BilR is readily found in the gut microbiome of healthy adults, further reinforcing its important role.
As for why it took so long to figure out how urine turns yellow, Hall points out that studying our tiny intestinal tenants has historically been difficult.
“Unfortunately, studying gut bacteria can be difficult. The gut is a hypoxic environment, and many of the bacteria in the gut cannot survive in too much oxygen, making them difficult to grow and experiment with in the lab. “It will be,” he said. “While our work to discover BilR relied on a combination of experimental screening and genomic analysis, this approach is only made possible by the isolation of more enterobacterial species and advances in genome sequencing technology. became.”
It’s important to answer basic questions about our biology. But the team’s efforts may pay off in other ways as well. They note that BilR is less common in neonates and patients with inflammatory bowel disease. It is also possible that gut microbiota that cannot produce BilR may contribute to neonatal jaundice and pigmented gallstones, both of which are strongly linked to excess bilirubin in the body.
Further research is needed to confirm the link between gut microbes, BilR, and these symptoms, Hall said, and the team is already planning to work on that. They next hope to conduct observational studies in humans to better understand how bilirubin reduction by gut bacteria affects bilirubin levels in the blood. And we want to specifically study premature infants who are at high risk of jaundice and have low BilR levels.