Media Recipes

Microbial growth media provides nutrients and energy sources that microbes need to grow and multiply. The recipes on this page have been developed for or adapted to suit the salt-loving microbes that live in Great Salt Lake. Each will make 1 L of liquid or solid media, but they can be scaled up or down as needed.

To make liquid growth media, assemble all the ingredients-leaving out the agar-and sterilize using one of the methods described on the Sterilizing Liquids page. To make solid media in Petri dishes, follow the instructions on the Making Agar Plates page.

Salt-loving microbes from Great Salt Lake will grow in media with 5-20% salt (that's 5-20 g of salt per 100 mL). One advantage of high-salt media is that typical contaminating microbes won't grow on it. Media with a salt concentration of at least 10% can be sterilized by boiling either in a microwave or on a hot plate (see the Sterilizing Liquids page).

LB (Lysogeny Broth)

LB is a common nutrient-rich media for growing bacteria. Tryptone and yeast extract are on the expensive side, and you will need to order them from a lab supply store. But the extra cost buys you a high-quality, consistent media.

For added convenience, you can also buy pre-mixed dehydrated LB ($73.50 for 500 g from Carolina). Just add water and extra salt.

  • 10 g Tryptone
  • 5 g yeast extract (available at natural food stores)
  • 50 g (for 5%) up to 200 g (for 20%) NaCl (can substitute non-iodized or sea salt)
  • 15 g agar (omit for liquid media)
  • Bring the volume up to 1 L with purified H2O
  • (Optional: some recipes suggest adjusting the pH to 7.0-7.5 with 5 N NaOH)

Beef Broth Media

This is a fairly nutrient-rich media that uses inexpensive grocery store ingredients. You can use beef bouillon mixed with the proper ratio of water (refer to the manufacturer's instructions) in place of the broth.

Be sure to use broth or bouillon without preservatives, or your microbes may not grow. Be sure to use clear broth, or strain out any flecks of herbs and spices, which students could mistake for microbial colonies.

  • 10 g sugar
  • 50 g (for 5%) up to 200 g (for 20%) non-iodized or sea salt
  • 15 g agar (omit for liquid media) *see Ingredient Notes
  • 500 mL beef broth
  • Bring the volume up to 1 L with purified H2O

Store-Bought Nitrogen-Rich Media #1

This recipe is from The Bug that Eats Toxic Waste (see reference below) and was formulated for the extreme halophile Halomonas campisalis. Miracle Grow® supplies extra nitrogen. Note that nutritional yeast is different from, and cannot substitute for, yeast extract.

  • 1.5 g Miracle Grow®
  • 1 g yeast extract (available at natural food stores)
  • 4 g Borax (sodium borate)
  • 10 g table sugar
  • 125 g non-iodized or sea salt (12.5%)
  • 900 mL purified H2O
  • Adjust pH to 9 with NaOH
  • 15 g agar (omit for liquid media) *see Ingredient Notes
  • Bring the volume up to 1 L with deionized H2O

Store-Bought Nitrogen-Rich Media #2

This recipe is from The Bug that Eats Toxic Waste (see reference below) and was formulated for the extreme halophile Halomonas campisalis. Miracle Grow® supplies extra nitrogen. Note that nutritional yeast is different from, and cannot substitute for, brewer's yeast.

  • Add 1 g brewer's yeast to 1 L of purified water; boil 15 minutes; let the solids settle out and pour the liquid portion into a clean container.
  • 1.5 g Miracle Grow®
  • 4 g Borax (sodium borate)
  • 10 mL corn syrup
  • 125 g non-iodized or sea salt (12.5%)
  • Adjust pH to 9 with NaOH
  • 15 g agar (omit for liquid media) *see Ingredient Notes

Ingredient Notes

Water

For best results, use water that is free of impurities, especially chlorine. Types of purified water include distilled, reverse osmosis, deionized, and ultrafiltered. Distilled water is available for purchase at most drug stores and grocery stores.

Agar vs. Gelatin

Many people are tempted to replace agar with gelatin as a low-cost alternative. But gelatin has some drawbacks.

  • Gelatin is less firm than agar, so the media will be fragile. Students may poke through the surface while trying to spread a sample.
  • You will need to store and incubate your plates media-side down, and they will melt in a 37 °C incubator.
  • Some bacteria can digest gelatin (they can't digest agar), turning the plates to mush.
  • Gelatin doesn't set properly in media with 10% or more salt.

Types of Agar

Less expensive, food-grade agar is available at Asian markets or the international section of specialty grocery stores (look in the Asian food section). Food-grade agar usually works fine, but consider spending a little more money and buying lab-grade agar. It produces more consistent and higher quality plates, and it is less often contaminated with bacteria or mold spores.

Resources

Dillon, D., Schumacher, B., Peyton, B. (1998), The Bug That Eats Toxic Waste. Developed at the Department of Chemical Engineering, Washington State University, Pullman, WA. Retreived from http://www.chbe.montana.edu/bpeyton/documents/courses/Teaching%20Module.pdf