Widely used in microbiology and molecular biology as a fluorescent substrate for detecting β-glucuronidase (GUS) enzyme activity. Its primary application is in the identification and quantification of Escherichia coli and other coliform bacteria in environmental, food, and water samples. When cleaved by β-glucuronidase, it releases a fluorescent compound—4-methylumbelliferone—that can be easily detected under UV light, enabling rapid and sensitive analysis. Commonly incorporated into culture media or assay kits for high-throughput screening. Also used in transgenic plant research where the GUS reporter gene is introduced to monitor gene expression patterns. The trihydrate form ensures stability and solubility in aqueous assay systems.