S-Gal^®/LB Agar Blend

S-Gal^® (sodium salt) is an autoclavable, water-soluble, chromogenic substrate for β-galactosidase, used to determine the presence or absence of a cloned DNA insert in bacteria growing on agar plates. S-gal^® is designed to replace X-Gal in blue-white selection of recombinant bacterial colonies with the lac+ phenotype.

Suitable for use in selection of recombinant bacterial colonies with the lac+ phenotype. S-Gal^® (sodium salt) is water-soluble, autoclavable and can be added to bacterial broth containing agar prior to autoclaving.

S-Gal^®/LB Agar Blend has been used for the identification of recombinant bacterial colonies.

When S-Gal^® is cleaved by β-galactosidase, the resulting product will chelate ferric ion to create a black, insoluble precipitate. Lac+ colonies grown in the presence of S-Gal^® and ferric ion turn an intense black color, allowing for easy differentiation between lac+ and lac- colonies.

Suspend contents of one packet in 500 ml distilled or deionized water. Sterilize by autoclaving for 15 to 20 minutes at 121-124°C. For microwaving, heat suspended mix until initial boiling. Mix well. Heat for short intervals with mixing until agar component is in solution. Do not allow boiling for extended periods of time. Antibiotics should be added following autoclaving or microwaving, after cooling to 48-52°C.

Ingredients (g/L)
Tryptone, 10
Yeast extract, 5
Sodium chloride, 10
Agar, 12
S-Gal, 0.3
Ferric ammonium citrate, 0.5
IPTG, 0.03

The ferric or Fe³⁺ ion is required for color development and must be added to any S-Gal^®
formulation. A medium prepared with S-Gal^® is moderately dark due to the presence of ferric ammonium citrate. This darker background often provides enhanced contrast for automated colony counting or isolation.

S-GAL is a registered trademark of Merck KGaA, Darmstadt, Germany