Storing E. coli -20 or -70

Jim Kami jakami at
Mon Nov 25 14:32:40 EST 2002

    A small question; is it really necessary to store frozen, permanent
E. coli cultures at -70C or will they do just as well at -20C ? The
cultures are frozen at -70 in a 4% glycerol "freezing media" (LB + some
extra potassium salts) and, so long as they don't thaw, is there any
real benefit to keeping them that cold.
    This is becoming an issue in our department in that we are now
storing several million cultures (BAC libraries) and the cost of
purchasing and running ultra-low freezer is starting to be a problem.
For the cost of two -70C freezers (~ $20,000) we could build a walk-in
-20 freezer with 10x the storage capacity.
    Also, if anyone knows if there is a way to keep permanent cultures
at room temp., that would solve all our problems. But I've not yet heard
of a practical method.

Thanks in advance.

Dr. Jim Kaki
Dept. of Agronomy and Range Science
University of California
One Shields Avenue
Davis, CA     95616-8515
Tel: (530) 752-9982
Fax: (530) 752-4361
email:  jakami at
"Why is common sense always the least common sense ?"

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