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M63 minimal media problems - (Jan/04/2014 )



I have been trying to make M63 minimal media using a standard recipe that is consistent across a number of protocol manuals and online sources.  Below is the recipe I have been trying:


For 1 liter of medium add:


2g          (NH4)2SO4

13.6g     KH2PO4

0.5g       FeSO4.7H2O

MilliQ water to 1L


Adjust to pH 7 using KOH

Autoclave, cool

Add 1mL 1M MgSO4


All seems to go well until I begin to adjust the pH using KOH.  As soon as I begin adding KOH the solution begins to turn a dark dingy gray and begins to flocculate a fluffy grayish-brownish precipitate. 


Any ideas on what I might be doing wrong or thoughts about how to correct this problem?


Thanks for any help.


If you are actually adding 0.5 g (not 0.5 mg?) of FeSO4, then you need to change to adding 0.5 mg.  Too much FeSO4 will precipitate, as will the Fe (III) hydroxide.


Coincide with bob1, too much iron for that pH. And it will be worse once autoclaved.


It's 0.5 mg FeSO4/L

-El Crazy Xabi-



Thanks so much for the help.  Foolish oversight on my part.