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Preparation of SOC (Super Optimal broth with Catabolite repression) Medium
SOC (Super Optimal broth with Catabolite repression) medium is a nutrient-rich microbial growth medium, formulated by Douglas Hanahan in 1983 (Hanahan, 1983). SOC medium is prepared without Mg++ and Glucose by dissolving 20 g bacto-tryptone, 5 g bacto-yeast extract, 2 ml of 5M sodium chloride, and 2.5 ml of 1M KCl in water to a final volume of ≈ 1000 ml (960 ml). Magnesium salts (i.e., MgSO4 and MgCl2, 10 ml each of 1M MgSO4 and 1M MgCl2) and Glucose (10 ml of 1 M Glucose) are added to the medium after autoclaving to prevent any chemical reactions and precipitation of the medium components, and degradation of Glucose.
Preparation of 1M Magnesium Chloride (MgCl2) Stock Solution
Magnesium Chloride (MgCl2) is soluble in water. Magnesium chloride is available in anhydrous as well as hydrated forms. Since anhydrous Magnesium chloride is hygroscopic (quickly absorbs water from the air), it is convenient to use hydrated forms that are easy to weigh out the right amount accurately. For this reason, Magnesium chloride hexahydrate (MgCl2.6H2O, Molecular Weight: 203.30) is often used to prepare a 1 M Magnesium chloride solution. A 1M stock solution can be prepared by dissolving 203.3 g of MgCl2.6H2O (Molecular Weight: 203.30) in water to a final volume of 100 ml. In the following section, we describe a procedure to prepare 100 ml of 1M MgCl2 stock solution.
Preparation of LB Luria Broth
LB is a rich growth medium, commonly used to grow E. coli. LB Luria Broth contains 1% Bacto-tryptone, 0.5% Bacto-yeast extract and 0.05% Sodium chloride. A 1000 ml LB Luria Broth is prepared by dissolving 10 g Bacto-tryptone, 5 g Bacto-yeast extract and 0.5 g sodium chloride in deionized water to a final volume of 1000 ml. After adjusting the pH 7.0 with 5N NaOH medium is autoclaved and stored in a cold room.
LB (Lysogeny Broth) Medium
LB (Lysogeny broth or Luria-Bertani) is the most commonly used growth medium for E. coli culture. LB is a rich medium that contains tryptone, yeast extract and sodium chloride. It promotes fast growth of E. coli in culture by fulfilling all nutritional requirements, thus suitable for all regular molecular biology applications including molecular cloning, plasmid amplification, and recombinant protein production. Several versions of the original recipe formulated by Giuseppi Bertani in 1951 are now in common use: Miller broth, Lennox broth, Luria broth. They differ in NaCl concentration.
Preparation of SOB (Super Optimal Broth) Medium
SOB (Super Optimal Broth) medium is a nutrient-rich microbial growth medium, designed by Douglas Hanahan in 1983. SOB or its glucose-supplemented version SOC is often used during transformation of E. coli competent cells with plasmids (added in transformed cells after heat shock). It results in better survival and higher transformation efficiency as compared to regular LB medium. It contains 2% Bacto-tryptone, 0.5% Bacto-yeast extract, 0.05% Sodium chloride, 2.5 mM KCl, and 10 mM MgCl2. A 1000 ml SOB medium is prepared by dissolving 20 g bacto-tryptone, 5 g bacto-yeast extract, 0.5 g sodium chloride and 2.5 ml of 1M KCl in water to a final volume of 1000 ml. Medium is sterilized by autoclaving. MgCl2 (5 ml of 2M MgCl2) is added just before use.