Super Optimal Broth

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Super Optimal Broth (SOB medium) is a nutrient-rich bacterial growth medium used for microbiological culture, generally of Escherichia coli. It was developed by Douglas Hanahan in 1983 and is an adjusted version of the commonly used LB media (lysogeny broth). Growth of E. coli in SOB or SOC medium results in higher transformation efficiencies of plasmids.[1][2]

Super Optimal broth with Catabolite repression (SOC) is SOB with added glucose.[3]



(Figures in parentheses are the weight required to create 1 liter of medium)



In addition to the SOB contents, SOC also contains

Alternatively, SOC can be made by adding small amounts of concentrated magnesium chloride and glucose solutions to pre-prepared SOB.

pH adjustment

For maximum effectiveness, SOB/SOC media should have its pH adjusted to 7.0 by adding concentrated sodium hydroxide.[5]


Finally, the SOB medium should be autoclaved at 121 °C to ensure sterility. SOC medium should not be autoclaved because the high temperature can cause the glucose to react with tryptic peptides (see Maillard reaction). SOC can instead be filter sterilized through a 0.22 µm filter. Alternatively, SOB and magnesium and glucose additive solutions can be autoclaved separately and mixed afterwards to final concentrations.


  1. ^ Hanahan, D. (1983). "Studies on transformation of Escherichia coli with plasmids". Journal of Molecular Biology 166 (4): 557–580. doi:10.1016/S0022-2836(83)80284-8. PMID 6345791. edit
  2. ^ a b SOC Medium
  3. ^ [1]
  4. ^ SOC medium
  5. ^ [2]