Freezing Bacteria-Liquid N2 OK?

Rafael Maldonado rafael at
Fri Mar 17 21:44:30 EST 1995

On Fri, 17 Mar 1995, Kimberly Baldwin wrote:

> Hello All,
> I was wondering about the feasability of storing frozen bacterial stocks
> under liquid nitrogen vs. storing at -80oC.  Are the cells viable?  Should
> they first be frozen slowly prior to storing under liquid nitrogen?  Or is
> snap freezing them okay?  Should they be frozen as glycerol stocks-or is
> DMSO or DMF okay to use instead?  I have always in the past stored them at
> -80oC (in glycerol or  with DMSO). 

You can keep bacterial cells under N2 if you want. -80 is enough to keep 
them during years; I suppose in N2 (-120, I think) they will be viable 

DMSO is more convenient: it's easy to handle, it don't need autoclaving 
and the cells are viable longer; just add at 7% v/v and freeze. I never 
used DMF, it's new to me. I'm surprised of seeing in storage cells medium.

Always freeze the cells as faster as you can. The faster way is N2;
a slow feezing process will kill more cells than a fast one. EtOH-dry ice 
baths are pretty fast too. 
Anyway, putting the tube directly at -80 works fine for most purposes. If 
the viabilty decresase 10% doing that, you still have 10^6 cells in 1 ml 
vial. That is enough for 20 years of keeping at -80, using DMSO. The limit 
with glycerol is around 10 years.

Those data are for E. coli and S. typhimurium.


Rafael Maldonado			"You gave to a boy the job  
Department of Human Genetics		 of a man. He's dead."
University of Utah			
Salt Lake City, Utah 84112. USA.	                     John Wayne
Rafael at
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