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op-50 genotype

Creg Darby cdarby at stanford.edu
Fri Sep 13 16:20:54 EST 2002

Because of the sort of presumed spontaneous mutation that Leon describes
below, your OP50 and his and mine may all be different. I tested two
different vials of OP50 in one lab's collection, obtained at different
times, and found that one was a uracil auxotroph and the other a uracil
prototroph. On another occasion, a potential food problem led the lab to
send away to CGC for a fresh stock of OP50, only to find that its texture
on plates was different from, and inferior to, what everyone was used to.

Two thoughts:

1. If the genotype of your food is important to you, it might be better to
switch to a better-characterized E. coli. Some labs, for instance, use
DH5-alpha, which also makes thin lawns that are compatible with worm
observation. Cloning strains of E. coli are generally wimpy, and many of
them would probably make good worm lawns.

2. Keep your food frozen, and *frequently* take a fresh thaw, streak for
single colonies, and inoculate single colonies into broth to make food.
Don't passage food by inoculating fresh broth with the dregs of older
stock -- it's convenient, but it's almost sure to change the
characteristics of the bacteria.

Creg Darby
Department of Microbiology
University of Alabama at Birmingham
creg at uab.edu

On 12 Sep 2002, Leon Avery wrote:

>  >Does anyone know the genotype of OP-50?
>  I once wrote to Brenner to ask this question.  I then lost his
>  response (brilliant!), but I think I remember the gist: it is a
>  uracil auxotroph of a non-K12 E coli strain (E coli B, I think).  So,
>  it is not a genetically well-characterized strain.  As Brenner's 1974
>  paper explains, a uracil auxotroph was chosen because prototrophs
>  tend to produce inconveniently thick lawns.  I also remember from
>  conversation in the Horvitz Lab some 15 years ago that OP50 is a bit
>  leaky -- the idea was that it would be able to grow slowly in the
>  absence of uracil, rather than being completely blocked.  OP50 tends
>  to produce snakes, a known characteristic of E coli unable to make
>  thymine (because growth continues while replication is blocked), and
>  spontaneous faster-growing colonies that I isolated from NGM plates
>  did not have this characteristic.  However, they also failed to grow
>  on minimal medium, to my surprise.
>  --
>  Leon Avery                                        (214) 648-4931 (voice)
>  Department of Molecular Biology                            -1488 (fax)
>  University of Texas Southwestern Medical Center
>  6000 Harry Hines Blvd                            leon at eatworms.swmed.edu
>  Dallas, TX  75390-9148                  http://eatworms.swmed.edu/~leon/
>  ---

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