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M9 minimal medium


Autoclave for sterilization:

  • 2.5g MgSO4 in 100ml ddH2O (final concentration 0.1M) = 50x stock

  • 1.1g CaCl2 in 100ml ddH2O (final concentration 0.1M) = 1000x stock

  • 28.2g M9 Salts (5×) in 500ml ddH2O = 5x stock

  • 10g Casamino acids in 100ml ddH2O = 50x stock

Filter sterilise:

  • 10g Fructose in 50ml ddH2O  (20%) = 50x stock


  1. M9 salts mix includes phosphates salts needed for the production of nucleotides for DNA and RNA synthesis. Also, it includes ammonium salts that provides the nitrogen for amino acid synthesis.

  2. Casamino acids are not essential since amino acid synthesis can proceed with ammonium salts. However, by supplying the amino acids the cell avoids needing to produce the myriads of enzymes required for ammonia acid biosynthesis.

  3. Other carbon sources can be used as well, for ex. glucose, glycerol etc.

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