Super Optimal Broth (SOB) or SOB + Catabolite repression (SOC) are rich media used for the culturing and recovery of chemically competent E. coli. SOB is usually used for the culturing and SOC for recovery.
Dissolve the following with a stir bar:
- 20 g/L tryptone
- 5 g/L yeast extract
- 0.5 g/L NaCl
- 0.746 g/L KCl (final 2.5 mM)
- sufficient water, subtracting additive volumes below
Measure the pH; it is usually at or slightly above 7.0, so the traditional protocol instructing adjusting pH to 7.0 with NaOH is usually moot. Autoclave on the 15 min liquid cycle for ≤1 L, 20 min for 1–1.4 L.
Add sterile MgCl2 and MgSO4 to a final 10 mM each. For a recovery medium, you may choose just one of these, as 10 mM is sufficient Mg. The chloride salt is slightly superior. Omit glucose for SOB; add glucose for SOC
- 10 mM MgCl2: 10 mL/L 1 M, or 5 mL/L 2 M
- 10 mM MgSO4: 10 mL/L 1 M, or 5 mL/L 2 M
- 20 mM glucose: 20 mL/L 1 M, or 18 mL/L 20% m/V (For SOC only)