Super Optimal Broth

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 masses required to create 1 liter of medium)


  • 2% w/v tryptone (20 g)
  • 0.5% w/v Yeast extract (5 g)
  • 8.56mM NaCl (0.5 g) or 10mM NaCl (0.584 g)
  • 2.5mM KCl (0.186 g)
  • ddH2O to 1000 mL[4]
  • 10mM MgCl2 (anhydrous: 0.952 g; hexahydrate: 2.033 g) AND 10mM MgSO4 (anhydrous:1.204 g; heptahydrate: 2.465 g)[2]


In addition to the SOB contents, SOC also contains 20mM glucose (3.603 g)

Alternatively, SOB and 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.[3] The original literature states that the pH of the final medium should be between 6.8 and 7.0.


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


  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.
  2. SOC Medium
  3. SOC medium
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