SOC Medium
Super Optimal broth with Catabolite repression — recovery medium for E. coli transformation
SOC Medium is a rich, low-salt broth used for the outgrowth of E. coli cells after chemical transformation or electroporation, giving higher colony yields than LB. It was described by Hanahan (1983). AS-1428 is the dehydrated SOB base; you add sterile glucose after autoclaving to make SOC.
Also known as: S.O.C. Medium, SOC Broth, Super Optimal Catabolite broth.
Why SOC Improves Transformation Yield
After heat shock or electroporation, cells need a short outgrowth period to repair their membranes and express the antibiotic-resistance gene before they meet selective plates. SOC supports this with rich nutrients (tryptone and yeast extract), 20 mM Mg²⁺, low salt and 20 mM glucose as an immediately usable energy source. Manufacturers commonly report about two-fold more transformants after outgrowth in SOC than in LB.
Tryptone and yeast extract support fast recovery
20 mM Mg²⁺, as in Hanahan's formulation
20 mM glucose, added after autoclaving
Composition (per litre of final SOC)
Final pH 7.0 ± 0.2 at 25 °C. Hanahan's original SOC supplies the 20 mM Mg²⁺ as 10 mM MgCl₂ plus 10 mM MgSO₄; AS-1428 supplies it as MgSO₄.
Related Media
| Medium | NaCl (g/L) | Glucose | Mg²⁺ | Main use |
|---|---|---|---|---|
| SOC (AS-1428) | 0.5 | 20 mM | 20 mM | Outgrowth after transformation |
| SOB | 0.5 | None | 20 mM | Growing cells for competent cell preparation |
| LB Lennox / LB Miller | 5 / 10 | None | None | Routine E. coli culture and selection |
| 2×YT | 5 | None | None | Phage and M13 work |
| Terrific Broth | None | None (glycerol) | None | High-density culture and protein expression |
Comparable Products
| Supplier | Product | Relationship |
|---|---|---|
| AuSaMicS | SOC Medium, dehydrated base (AS-1428) | — |
| Invitrogen (Thermo Fisher) | S.O.C. Medium, ready to use (15544034) | Comparable published formulation |
| Sigma-Aldrich (Merck) | SOC Medium, ready to use (S1797) | Comparable published formulation |
Based on published formulations. Trademarks belong to their respective owners.
Strengths and Limitations
Strengths
- ✓ More transformants than outgrowth in LB
- ✓ Standard recovery medium in most cloning protocols
- ✓ Glucose-free base can also be used as SOB
- ✓ Dehydrated format: prepare only what you need
Limitations
- ▲ Extra step: glucose must be added aseptically
- ▲ Not a selective medium: use antibiotic plates afterwards
- ▲ Not intended for yeast transformation recovery
- ▲ Higher cost than LB for routine culture
Frequently Asked Questions
What is SOC medium used for?
SOC is used for the outgrowth of E. coli after chemical transformation or electroporation. Cells recover and express the resistance gene before plating, which gives more transformants than LB.
What is the difference between SOC and SOB?
SOB contains no glucose. SOC is SOB plus 20 mM glucose, added after autoclaving. AS-1428 is the glucose-free base, so it can be used as SOB or made into SOC.
Why is glucose added after autoclaving?
Heating glucose with peptones causes browning (Maillard reaction) and degrades nutrients. Sterilise the glucose separately, preferably by 0.2 µm filtration, and add it to the cooled base.
How much glucose do I add to make SOC?
Add 20 mL of sterile 1 M glucose (18% w/v) per litre, giving 20 mM (3.6 g/L). Using 20 mL of 20% glucose gives 22 mM (4.0 g/L), which is slightly higher than Hanahan's formulation.
How long should cells recover in SOC?
Typically 1 hour at 37 °C with shaking. Follow the protocol supplied with your competent cells, as some recommend different times.
Mode of Action
Transformation leaves E. coli cells stressed, with damaged membranes and depleted energy. During outgrowth in SOC, tryptone and yeast extract supply amino acids, vitamins and nucleotides, glucose provides a readily used energy source, and magnesium supports membrane and ribosome function. Cells repair, resume growth and express the plasmid's resistance gene before plating on selective media.
Physical and Chemical Specifications
Typical Transformation Protocol
- After heat shock (e.g. 42 °C, 30–45 s) or electroporation, add 250 µL to 1 mL of room-temperature SOC.
- Incubate at 37 °C for 1 hour with shaking at about 225 rpm.
- Spread on selective agar plates and incubate overnight at 37 °C.
Follow the protocol supplied with your competent cells when it differs.
Recommended Control Strain
Storage
Dehydrated base: Store at 15–25 °C in a dry place with the container tightly closed. Use before the expiry date on the label.
Prepared SOC: Store at 2–8 °C, or in single-use aliquots at −20 °C. Discard if cloudy. Validate the storage period in your laboratory.
References
- Hanahan D. Studies on transformation of Escherichia coli with plasmids. J Mol Biol. 1983;166(4):557–580.
- Green MR, Sambrook J. Molecular Cloning: A Laboratory Manual. 4th ed. Cold Spring Harbor Laboratory Press; 2012.
- Inoue H, Nojima H, Okayama H. High efficiency transformation of Escherichia coli with plasmids. Gene. 1990;96(1):23–28.
- Görke B, Stülke J. Carbon catabolite repression in bacteria: many ways to make the most out of nutrients. Nat Rev Microbiol. 2008;6(8):613–624.
Safety Summary
The full 16-section SDS is available for every lot on request from support@ausamics.com.