It is a substrate for beta-galactosidase, which cleaves the glycosidic bond to give 5-bromo-4-chloro-3-hydroxy-1H-indole, which immediately dimerises to give an intensely blue product. It is also used to detect activity of this enzyme in histochemistry and bacteriology. It is employed as a colorless, endogenous or exogenous pigment precursors that may be transformed by biological mechanisms into colored compounds. They are used in biochemical assays and in diagnosis as indicators, particularly in the form of enzyme substrates. X-Gal is the substrate of choice for blue-white selection of recombinant bacterial colonies with the lac+ genotype.
Christiaen L, et al. X-gal staining of electroporated sea squirt (Ciona) embryos.Cold Spring Harbor protocols.20092009(12), prot5346.
Kim MY, et al. X-gal inhibits the swarming of Vibrio species.J. Microbiol. Methods.200666(3), 552-555.