From owner-celegans@net.bio.net Sun Sep 08 23:00:00 1996
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From: phil@omega.uta.edu (Patrick Phillips)
Newsgroups: bionet.celegans
Subject: Re: M9 precipitate
Date: 9 Sep 1996 14:02:25 GMT
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I had this problem for several years, but was too embarrassed to ask 
about it since I figured all the "in" worm people would know what was
wrong (sounds like the makings of a good TV commercial).  Anyway, the
culprit seems to be the magnesium sulfate solution.  It must react with
another salt when hot (I never figured out which one).  This is
presumably why you need to add the salts after autoclaving in NGM too.
We have therefore slightly modified the book recipe by adding the MgSO4
after autoclaving.  Works great now.  It is a bit of a pain since we
aliquot to 50ml bottles before autoclaving.  (Thanks to Phil Anderson's
old recipe cards for helping me figure this one out).

On a related note, what exactly is the history of these solutions?  I
believe that M9 is originally from bacterial culture (some recipes I've
seen call for glucose, for instance).  Was M9 ever optimized for worms,
or just taken over from the microbiology literature?  The reason I ask
is that it seems very salty (judged by taste), and it is not clear that
it is isotonic with the worms (never tasted the worms :-).  The worms
don't always seem happy after long periods in M9 (say longer than an
hour).  Of course many people just use S-basal instead.  Is the choice
between these two all just individual preference and history?
---------------------------------------------------------------------
Patrick C. Phillips               pphillips@uta.edu
Biology Department, Box 19498     http://www.uta.edu/biology/phillips
University of Texas at Arlington  Tel. (817) 272-2409
Arlington, TX 76019 USA           FAX  (817) 272-2855
            Genes in theory, Worms in practice.

.