Team:UNIPV-Pavia/Methods Materials/XGal




X-Gal staining protocol for beta galactosidase (blue/white screening)

(Estimated time: 20 min)

  • The principle is that X-Gal (5-bromo-4-chloro-3-indolyl-b-D-galactopyranoside) turns blue when reacts with beta-galactosidase.
  • Mix 20 ul X-Gal 20 mg/ml and 80 ul SOC and spread on LB+amp plates (X-Gal and DMF are toxic, use face-mask for your safety!!! X-Gal is light-sensitive, remember to keep it in the dark, when possible)
  • Incubate with 200 ul bacteria
  • Result: blue colonies express LacZ, while white colonies don't.


40 mg/ml X-gal in DMF
SOC medium
Pre-warmed LB agar plate

Face mask