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S-Gal®/LB Agar Blend

reagent for selection of recombinant bacterial clones



for molecular biology

Quality Level






suitable for β-galactosidase test
nonselective for Escherichia coli
nonselective for coliforms


food and beverages

storage temp.

room temp

Related Categories

General description

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.


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


500, 500 mL

Features and Benefits

  • More intense color contrast than X-gal
  • Water-soluble and autoclavable for easiest use
  • Convenient, pre-mixed media


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


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.

Preparation Note

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.

Other Notes

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.

Legal Information

S-GAL is a registered trademark of Sigma-Aldrich Co. LLC

Storage Class Code

11 - Combustible Solids



Flash Point(F)

Not applicable

Flash Point(C)

Not applicable

Personal Protective Equipment

dust mask type N95 (US), Eyeshields, Gloves

Certificate of Analysis

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Certificate of Origin

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