SOC medium

Media & solutions

Rich recovery medium for transformed bacteria. Higher transformation efficiency than LB. Use 1 mL per chemical or electro-transformation reaction.

Recipe (1 L)

Tryptone — 20 g
Yeast extract — 5 g
NaCl — 0.5 g
KCl — 0.186 g (2.5 mM final)
Deionized water to 980 mL

After autoclaving — add filter-sterilised:

2 M MgCl₂ — 5 mL (10 mM final)
2 M MgSO₄ — 5 mL (10 mM final)
1 M glucose — 20 mL (20 mM final)

Procedure

Dissolve tryptone, yeast extract, NaCl, KCl in 980 mL water.
Autoclave 121 °C, 20 min.
Cool to room temperature.
Add MgCl₂, MgSO₄, and glucose stocks (filter-sterilised, 0.22 µm).
Aliquot 1–2 mL into sterile 1.5 mL or 2 mL tubes. Store at −20 °C for up to a year.

Notes

Glucose must NOT be autoclaved with the rest — it caramelises and reduces transformation efficiency.
If pressed for time, LB works in a pinch but expect a 2–5× drop in transformation efficiency.
For very low-yield transformations (e.g. recombineering), pre-warm SOC to 37 °C before adding to cells.