6-Chloro-3-indolyl b-D-galactopyranoside

6-Chloro-3-indoxyl-beta-D-galactopyranoside is a chromogenic substrate for beta-galactosidase that yields a salmon or rose-coloured precipitate and hence is also known as Salmon-Gal. It can be used in conjunction with isopropyl-beta-D-thiogalactopyranoside (IPTG) as an alternative to the chromogenic substrate 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside (X-Gal) for detection of beta-galactosidase activity in bacterial colonies in colorimetric assays. Where beta-galactosidase expressed from a reporter gene in molecular biology experiments, recombinant colonies on growth plates are salmon-coloured while non-recombinants appear as white. Use of nitroblue tetrazolium salt (NBT) with Salmon-Gal may provide faster results, yielding a clear, purple precipitate, than for Salmon-Gal alone. In conjunction with 5-bromo-4-chloro-3-indolyl-beta-D-glucoside (X-Glc), Salmon-Gal is useful for simultaneous detection of GUS and Lac activities in the same medium.