← All protocols

LB liquid medium

Media & solutions

Lysogeny Broth (Lennox formulation) — the workhorse medium for routine E. coli growth, cloning, and transformation recovery.

Recipe (1 L)

• Tryptone — 10 g
• Yeast extract — 5 g
• NaCl — 5 g (Lennox); use 10 g for the Miller formulation
• Deionized water to 1 L

Procedure

1. Dissolve dry components in ~900 mL of deionized water in a 2 L Erlenmeyer flask or autoclavable bottle. Stir until clear.
2. Bring to 1 L final volume with deionized water.
3. Cap loosely (foil + autoclave tape) and autoclave at 121 °C, 20 min, liquid cycle.
4. Cool to room temperature before use. Store at room temperature for ~1 month or 4 °C for ~6 months.

Adding antibiotics

Cool the medium to ≤ 55 °C before adding antibiotic stock — heat destroys most antibiotics. See antibiotic stock solutions for working concentrations.

Notes

• If using a pre-mixed LB powder (e.g., Difco), follow vendor directions — typically 20–25 g/L.
• For minimal/defined growth, switch to M9 + supplements rather than LB.
• Cloudiness after autoclaving suggests precipitation; usually fine to use, but check pH (~7.0) if cells grow poorly.