I made up three separate solutions of M9 minimal media adding the components in the following order (total volume 200ml) and then adjusted the pH to 7, 7.4 and 7.8

1. 40ml M9 salts (5x)

2.400ul MgSO4

3. 4ml 20% glucose

4. 20ul CaCl2

5. 156ml deionised water

However, after adding the CaCl2 I found that it precipitated. Any idea why? I am thinking it could be a problem in the order of adding the components.

In addition to this, I autoclaved the solution and when it finished the cycle the media had turned yellow. Is this indicative of contamination or is this normal?

Thanks for your help,

Michael