Knight:Beta-galactosidase assay/Fluorescence

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See beta-galactosidase assay for other methods.

This method uses 4-Methylumbelliferyl beta-D-galactopyranoside (MUG) for lacZ detection (Sigma M1633). MUG has the advantage that it gets into the cell. MUG can be detected via fluorescence using 360nm/460nm


  • 2 mg/ml MUG in DMSO. Use as 10x (final concentration 200 μg/ml)


  • It works to grow liquid cultures with MUG. The fluorescence is easily detected on a normal UV box (cells look blue)
  • The MUG can be directly substituted for ONPG in a Miller-type assay
  • It is highly amenable to reading on a plate reader in 96-well format
  1. Vidal-Aroca F, Giannattasio M, Brunelli E, Vezzoli A, Plevani P, Muzi-Falconi M, and Bertoni G. One-step high-throughput assay for quantitative detection of beta-galactosidase activity in intact gram-negative bacteria, yeast, and mammalian cells. Biotechniques. 2006 Apr;40(4):433-4, 436, 438 passim. DOI:10.2144/000112145 | PubMed ID:16629389 | HubMed [Vidal-Aroca-2006]