Screening principle of bacterial blue-white spots:

IPTG is a placebo inducer that can induce the production of alpha-galactosidase, and x-gal is the substrate of alpha-galactosidase. Under the action of alpha-galactosidase, x-gal is cut into galactosidase and dark blue substance: 5-bromo-4-indigo, colored substances can make the colony appear blue.

working concentration：

IPTG concentration: 50mg/ml;X-gal concentration: 20mg/ml

Direct coating:

10l of IPTG solution and 20l of x-gal solution were added to the medium, and 50 ~ 100l of sterile water or sterile LB was added at the same time.

prefabricated slab：

When the plate is inverted, the temperature drops to 50℃.250l of IPTG solution and 500 mg per 100mlLB?L of the x-gal solution, after mixing the plate can be made.

attention：

1. X-gal was insoluble in water and was dissolved in dimethylformamide (DMF);

2. X-gal is sensitive to light, and the plate containing x-gal should be kept away from light and used within 1 to 2 weeks;

3. After overnight culture, the blue-white spot is not obvious. The plate can be put into the refrigerator at 4℃.