WENDY CHAO'S LABORATORY PROTOCOLS

MICROWAVE-STERILIZING MEDIA - forget the low-tech, time-consuming autoclave!

There was a whole Biotechniques article about this subject, but really doesn't require much thought. I've been sterilizing LB media for years in the microwave. It's way faster than autoclaving, and just as effective. To prevent the media from boiling over in the microwave, make sure the dry ingredients are completely dissolved before microwaving - it helps to pre-boil the water before adding the dry stuff.

Recipe for Luria-Bertani (LB) broth/media

• Bring 950 ml deionized water to a boil in the microwave
• Dissolve completely:
  • 10 g peptone from casein
  • 5 g yeast extract
  • 10 g NaCl
• Adjust pH to approximately 7.0 with 0.2 ml 5N NaOH
• Add dH₂O to 1 liter
• Boil in microwave for about 5 minutes with the cap loose. Make sure the media does not boil over; if it does you should pour the media into a clean bottle and re-boil. You may have to split the media up in 2 500-ml bottles to they can fit into the microwave oven.
• Tighten cap and store at room temperature.

The only trick here is dissolving the dry ingredients completely before microwaving the media again, otherwise the media will boil over in the microwave. If you hate cleaning the microwave oven as much as I do, don't microwave undissolved media!