SOC media recipe

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    Introduction

    SOC (Super Optimal broth with Catabolite repression) is a variant of SOB media. SOC is a nutrient-rich culture media developed by Douglas Hanahan in 1983. SOC is typically used for bacterial transformation. Since it is nutrient-rich media, it helps bacteria to recover faster after heat shock or electroporation.

    Applications

    SOC medium is optimized for growing transformed bacteria (E.coli).

    pH

    The SOC medium pH is adjusted to 6.8 - 7.0 with NaOH and HCl. Approximately 1-2mL of 1N NaOH is required for adjusting 1L of the medium.

    Composition

     

    Reagent M.W Working concentration Composition for 1L
    Tryptone NA 2 % 20 g
    Yeast extract NA 0.5 % 5 g
    NaCl 58.44 10 mM 0.5 g
    KCl 74.55 2.5 mM 0.18 g

     

    Reagent M.W Working concentration Stock concentration Add from stock for 1L
    MgCl2 95.2 10 mM 2 M 5 ml
    MgSO4. 7H2O 246.47 10 mM 2 M 5 ml
    Glucose 180.15 20 mM 2 M 10 ml

     

    Reagents

    • Tryptone
    • Yeast extract
    • NaCl
    • KCl
    • MgCl2
    • MgSO4.7H2O
    • Glucose
    • Bacto agar
    • NaOH

    Instruments and other requirements

    • Weigh dishes/paper
    • Petri dishes (optional)
    • Media bottle
    • pH meter
    • Autoclave
    • Balance
    • Measuring cylinders

    Procedure

    1.  Prepare stock solutions of Glucose and MgSO4, MgCl2 separately and filter sterilize them by using 0.22-micron membrane filter under laminar airflow chamber. Store them 4oC for long term use.
    2. Determine the volume to be made and weigh the remaining reagents required for the preparation of SOC, except MgSO4, MgCl2 and Glucose. The table above indicates the required mass to be weight.
    3. Add the reagents to a glass beaker and add de-ionized water up the volume to 90% of planned volume. For eg., if you plan to make 1L of the media, add 900 ml of water. The remaining volume to be adjusted after pH and other components if any. Note: While making up the final volume, reserve 2% of total volume for adding Glucose and MgSO4, MgCl2 at the end.
    4. Dissolve the components in the beaker using a magnetic stirrer.
    5. Adjust the pH to the desired value. (see the pH section above for details).
    6. Adjust the broth to final volume using de-ionized water.
    7. Transfer the broth to conical flask or aliquot into smaller volumes.
    8. Close the mouth of the flask with a cotton plug. Seal it further with paper and rubber band.
    9. Autoclave for 20 min at 15 psi (1.05 kg/cm2) on liquid cycle.
    10. After Autoclave, cool down the medium to room temperature under laminar airflow chamber.
    11. Add MgSO4, MgCl2 and Glucose stock solutions till the required working concentrations and mix thoroughly before use.

    Preparation of SOC Agar media

    1. If you plan to prepare solid media, add the add agar (1.5%; i.e., 3.75 g / 250 ml media) after step No 5 in the procedure.
    2. You can add MgCl2 and glucose just before the media gets solidified (~60oC). If the media is already solidified, bring it to 60oC using a water bath to add components.

    Storage

    SOC medium can be stored at room temperature and is stable for several months.

    Caution

    Do not add agar at this point if you are preparing solid medium.

    Before use, be sure to add the proper amounts of sterile glucose (20 mM final) and magnesium chloride (10 mM final).

    Reference