Lambda-agar is nothing but a lambda broth which is solidified by agar. Agar is a solidifying agent. It melts at 85°C but melton agar stays liquid at a temperature > 40°C (this property is called hysteresis, different temperatures for melting and solidifying). This allows us to add heat-labile medium supplements such as antibiotics and vitamins and prepare solid medium.
Lambda-agar solid medium is prepared by dissolving 15 g agar / liter of Lambda broth (Elbing & Brent, 2019). Whenever needed, solid medium is melted and plates are poured.
Here we describe a procedure to prepare 500 ml Lambda-agar solid medium that is sufficient to prepare ≈ 15 plates (≈ 30 ml medium/10 cm petri-plate).
Reagents and Solutions
Equipment and disposables
1x Lambda broth
Preparation of 500 ml of Lambda-agar medium
Step 1: Weigh out 7.5 g agar in a 1-liter Erlenmeyer flask/autoclavable bottle. Add 500 ml Lambda broth. Mix it by swirling the flask.
Step 2: Close the lid of the bottle loosely/insert a cotton plug and cover the mouth of the Erlenmeyer flask with aluminum foil.
Step 3: Sterilize the solution by autoclaving for 20 minutes at 15 lb/in2 (1.05 kg/cm2) on liquid cycle.
Lambda-agar medium (solid at room temperature) can be stored at room temperature for a few weeks but for a longer time, we recommend you to store it in the cold room.
Depending on your convenience, you can prepare the lambda-agar plate any time by melting the medium.
After autoclaving, the medium must be handled aseptically to maintain sterility.
Step 4: Allow the medium to cool below 50°C. If required, add supplements such as antibiotics. Mix by swirling the flask gently.
Step 5: Pour ≈ 30 ml medium per 10 cm plate. Let the medium solidify. Keep the plate open for 2 h at room temperature to dry the plate.
Remove the trapped air by touching with the needle/micropipette tip.
Don’t cover the plate with a lid. If the plate is covered with the lid, all the vapour will condense on the lid and form water droplets that eventually fall back to the solidified medium.
Cover the plates with their lid and store at 4°C in an inverted position.
- Elbing & Brent, 2019. Recipes and Tools for Culture of Escherichia coli. Curr Protoc Mol Biol. 125(1), e83. PMID-30412361; Full-Text Links: wiley, PMC