This media is used to screen Streptomyces strains for extracellular protease production. The resulting degradation of the milk powder components on the plate, which can be detected as protein degradation "halos", visually resemble zone of inhibtions that one would observe with bioassays. This recipe was adjusted for Streptomyces clavuligerus.
- 50 g Dry milk powder
- 5 g Tryptone
- 2.5 g Yeast Extract
- 12.5 g Agar
- 5 g Glucose (add glucose from stock solution after autoclaving)
- 1 L dH2O
- Dissolve all components (but glucose and agar) in 0.9 L dH2O
- Adjust pH to 6.8 - 7.0
- Add and dissolve agar
- Add 100 ml of a filtersterilised 50% glucose solution
- The milk powder in the media will curdle, mix gently by swirling bottle prior to pouring plates
- if alternative carbon sources are added to the media, adjust number of carbon atoms accordingly,
Example: add 10 g/L of glycerol (C3), or 2.5 g/L of maltose (C12)
After heat-activation and pre-germination of Streptomyces spores, they can then be spotted (~5µl )onto the agar for sharp edges of the colonies and the resulting protease halos. Once spotted, the plates are incubated at 26°C for Streptomyces clavuligerus or 30°C for other Streptomcyes strains.
Cheeseman, G. C. (1963) “Action of rennet and other proteolytic enzymes on casein in casein-agar gels,” Journal of Dairy Research. Cambridge University Press, 30(1), pp. 17–22. doi: 10.1017/S0022029900011213.