Talk:M9 salts

The 5x M9 salts recipe here seems to be almost identical to the 10x M9 salts protocol we use in our lab and which I also found elsewhere (see e.g. http://www.changbioscience.com/protocols/recipe/M9salts10X.htm and http://www.atcc.org/mediapdfs/2057.pdf). It could be that bacteria don't mind if they get the double of salts, but it might nevertheless be interesting to know what conc. of salts would be best to use... (MDolinar)

Miller Vs. Sambrook

At first I thought that this discrepancy may have arisen due to a miscalculation somewhere down the line brought about by the difference in molecular mass between Na₂HPO₄[math]\displaystyle{ \cdot }[/math]7H₂O and Na₂HPO₄, but I did a little digging and it seems that the real difference is who you trust more: Sambrook or Miller. The [Sambrook protocol] for 5x M9 salts uses 64g Na₂HPO₄[math]\displaystyle{ \cdot }[/math]7H₂O while the [Miller protocol for 5x calls for 30g Na₂HPO₄ (hence 60g Na₂HPO₄ in most 10x recipes).

In the end, the two recipes are only slightly different when you take the difference in hydration into account. When you make 1x medium from 10x Miller M9, you end up with ~42mM Na₂HPO₄, while 1x medium made from 5x Sambrook M9 leaves you with ~48mM Na₂HPO₄. Presumably, this is close enough.

References

J. Sambrook, D.W. Russell, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory Press, New York, ed. 3, 2001) pg. A2.2
J. Miller, Experiments in Molecular Genetics (Cold Spring Harbor Laboratory Press, New York, 1974) pg. 431