β-Galactosidase catalyzes the hydrolysis of glycosidic bonds in β-Galactopyranosides. In microbiology and molecular biology, the lacZ gene from E. coli (encoding β-Galactosidase) serves as a reporter gene as the hydrolysis of X-Gal (5-Bromo-4-chloro-3-indoxyl-β-D-galactopyranoside) produces a blue, water-insoluble indigo dye. Like this, the temporal expression of genes can be analyzed.