Super Optimal Broth (SOB) or SOB + Catabolite repression (SOC) are rich media used for the culturing and recovery of chemically competent competent E. coli and recovery following transformation. SOB is usually used for the culturing and SOC for recovery.
Not that the "super optimality" is only in the context of making chemically-competent and electrocompetent cells due to its minimization of monovalent ions and saturation of cell membranes with divalent Mg²⁺.
| Tryptone | – | 20 g/L | Dissolve with stir bar. |
| Yeast extract | – | 5 g/L | |
| NaCl | 10 mM | 0.584 g/L | |
| KCl | 2.5 mM | 0.186 g/L | |
| Milli-Q water | Reserve Mg soln volumes | ||
| NaOH, 1 M | → pH 7.0 | Check pH. typically not needed | |
| Autoclave 15 min ≤ 1 L, 20 min 1–1.4 L. Or filter sterilize* after adding components below. | |||
| MgCl2 sterile | 10 mM | 10 mL/L 1 M | autoclaved or filtered |
| MgSO4 sterile | 10 mM | 10 mL/L 1 M | autoclaved or filtered |
| Glucose sterile | 20 mM | 20 mL/L 1 M | For SOC only. Can be spiked-in. |
Store at 4° for best long-term preservation of nutrients. * Detergent-free membranes (PES, NYL, CN) are preferred for filter-sterilization. | |||
- Dissolve the following with a stir bar:
- 20 g/L tryptone
- 5 g/L yeast extract
- 0.
- 584 g/L NaCl (10 mM)
- 0.
- 186 g/L KCl (
- 2.5 mM)
- sufficient Milli-Q water, subtracting
- Mg and glucose volumes below
- Measure the pH; it is usually already 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.
- Or filter-sterilize after adding Mg solutions below, preferably with a detergent-free PES, NYL, or CN membrane.
- Add sterilized MgCl2 and MgSO4 to a final 10 mM each. For use as 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 sterile, or 5 mL/L 2 M
- 10 mM MgSO4: 10 mL/L 1 M sterie, or 5 mL/L 2 M
- 20 mM glucose: 20 mL/L 1 M,
- 18 mL/L 20%m/V (
- 200 g/L), or 7.2 mL/L of 50%m/V (500 g/L)
For SOC only; glucose can be spiked into SOB when needed, without regards for its volume.
- 200 g/L), or 7.2 mL/L of 50%m/V (500 g/L)
- Store at 4° for best long-term preservation of nutrients. Aliquots of SOC can be frozen to inhibit contaminant growth, unlike storage at 4° which can still allow contaminant growth.