Storage Temperature for Frozen Strains -45 vs. -70 ?

Model Organism: Worms Methods & Reagents
1

the protocols I have found for freezing C. elegans strains using a freezer (rather than liquid nitrogen) suggest using -70 degrees.

Before I try and persuade my department to buy a new -70 freezer, is there any emprical evidence that strains frozen using the accepted method are less viable when stored at a temperature of -45 degrees?

(Again, in the absence of the search function I have perhaps missed something in the forum archives).

The cost of a -45 degree freezer is such that I could buy 4 for the same price as a -70 (and have 2 or 3 back up freezers when one dies).

Regards

Steve

2

Hi Steve,

I am not sure how long your strains would last at -45. At -80, strains can last for years (http://www.wormbook.org/chapters/www_strainmaintain/strainmaintain.html) but a long term solution would be liquid nitrogen storage.

I think you’ll need to use a -80 at some point in time if you plan on putting your worms in liquid nitrogen since gradual freezing is required.

3

Hi Snug,

thanks for the link, I had read through the chapter and just wondered if it had to be so low. I have always frozen cells etc in the past at -70/-80 degrees. The only reference I could find that suggests why higher than -80 is problematic is from;

P Maher: Freezing of living cells: mechanisms and implications Am J Physiol Cell Physiol September 1, 1984 247:(3) C125-C142.

He suggests that at higher temperatures (for example -45 degrees), some liquid water still exists which can promote cell destruction. However, the mode of freezing and use of freezing solution must influence this I think.

Anyway, I guess I’ll have to bite the bullet and invest in a -80 freezer and a Dewar flask!

Thanks for your reply.

Regards

Steve