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[Celegans] Re: OP50 Problems

Sam Smith via celegans%40net.bio.net (by sasmon from gmail.com)
Thu Dec 2 10:03:38 EST 2010

On Dec 1, 2:46 pm, Sam Smith <sas... from gmail.com> wrote:
> We use OP50 and notice 2 problems.  One, we get "dots" of abnormal
> colonies within the main lawn.  Two, every once in a while the OP50 is
> a fast growing mass that has a thick crusty look to it rather than
> being a loose colony. We've done everything we can think of to resolve
> these problems, like constantly streaking new colonies for our LB,
> making smaller portions of LB so the OP is not very old (2 months),
> sterilizing any tools, and ordering new stock from the elegans
> center.
> Have others had this problem?  Is this most likely a contamination
> problem, or can the OP just be accumulating common mutations that
> result in this phenotype?
> The problem with this stuff is that with this crusty bacteria, it
> pellets with the worms and can't be separated.

I wanted to followup on the "crusty" bacteria situation.  I received
quite a few helpful responses; thank you all.  I think the most
plausible explanation is that there is too much Calcium in our plates
as our lab tech recently made - using the same OP50 stock - several
trays with this crusty stuff and 2 trays of perfect lawns.
Coincidentally, she also had to make new solutions of CaCl2 yesterday
because we were getting low.  I'm thinking that she made the good agar
first as the CaCl2 was getting low, then mixed the contents (as
usually there is some precipitate at the bottom of old bottles), and
voila: bad plates!  I'll need to watch this in the future to make
absolutely sure, but it really does seem to explain our problem.  I
hope this is helpful to your labs!

As for the "dots", the jury is out.  When I find out for sure, I'll

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