5X M9 salts (minimal medium) recipe
The salt stock for defined E. coli minimal medium, also used for isotope-labelled (¹⁵N, ¹³C) protein production.
🧮 Volume calculator
| Component | Amount | Final concentration (1X) |
|---|---|---|
| Na₂HPO₄·7H₂O | 32 g | 239 mM (5X) |
| KH₂PO₄ | 7.5 g | 110 mM (5X) |
| NaCl | 1.25 g | 43 mM (5X) |
| NH₄Cl | 2.5 g | 93 mM (5X) |
| Water (distilled) | to final volume |
Steps
- Dissolve in about 80% of the final volume of water.
- Bring to the final volume with water.
- Autoclave (121 °C, 20 min). Store at room temperature.
Good to know
- M9 minimal medium, 1 L: 200 mL 5X M9 salts + 2 mL 1 M MgSO₄ + 20 mL 20% glucose + 0.1 mL 1 M CaCl₂ + sterile water (each sterilised separately).
- For ¹⁵N labelling, omit NH₄Cl and add ¹⁵NH₄Cl (1 g/L) separately.
FAQ
Why add MgSO₄ and CaCl₂ separately?
They precipitate with phosphate when autoclaved together, so add them to cooled medium.
This is a widely used standard composition. Amounts depend on the hydrate form and purity of your reagents — check the formula weight (FW) on the bottle and follow your institution's safety rules and the manufacturers' instructions.