I had gone through the literature, every where they have mentioned that Glycerol stock we have to store @ -80C , But As the melting point of Glycerol is 17C. Is it OK to keep my glycerol stock in -20 or any other reason to do not store.
With Regards
If glycerol melts at -17, I wouldn't recommend -20 storage for a few reasons.
1) when you take the stock from the freezer, it will likely thaw (or at least start to) before you get it back to -20
2) freezers fluctuate temperatures (especially when opened). You risk your sample going through freeze-thaw cycles if this happens (even if on a small scale if part of the solution melts)
3) if you lose power it will be a lot faster to melt from -20 than from -80.
4) there is going to be a lot more chemical reactivity going on at -20 than at -80. Just because it's frozen doesn't mean it is inert.
Respected Matthew Sir
Accepted! Thank you very much for few reasons and kind reply.
But i wondered Is there any chemical re-activity @ -80C. Please kindly clarify me If so?
With Regards
there is going to be some activity at any temperature (well, to a point). A chemist could give you a more detailed answer (probably more accurate too), but basically the energy available at 37 (or 4, or -20) is greater than -80 so the chances of a chemical reaction taking place are (exponentially) higher.
Hi, first, to be correct, the melting point of pure glycerol is at +17.8 °C, not at -17 °C. Second, for long-term preservation of bacteria, you are probably not going put them into pure glycerol, but into a water-glycerol mixture (with something between 15% and 20% glycerol content). As you know, water melts at 0 °C. But when you mix water with glycerol, the melting point won't be in between the two melting points of the pure substances. Notably, glycerol is a non-ionic kosmotrope that forms strong hydrogen bonds with water molecules, thus competing with water-water hydrogen bonds. This disrupts the crystal lattice formation of ice unless the temperature is significantly lowered. The minimum freezing point temperature is at -37.8 °C at 70% glycerol in water... More info at Wikipedia: https://en.wikipedia.org/wiki/Glycerol
You normally store bacterial stocks in about 10-15% glycerol final concentration. The temperature will affect longevity. They store fine at -20C for some months (but not years) whereas at -80C they are stable for decades. So it very much depends upon your requirements, whether this is short term or long term storage. Also if storing at -20 you should be very careful to not use a frost-free freezer because those cycle the temperature above 0 every day to remove the ice as mentioned by Matthew.
Dear Anil, I would like to share the protocol for glycerol stock preservation. First subculture the microorganisms atleast 2 to 3 times. So, you can get the enough young cells. Then take 750 microlitre of the same aseptically in sterile cryovial. then add 250 microlitre sterile glycerol to it. Mix throughly and keep it at 37 c for half an hour. then preserve it at -20 or -70. Where ever you want to store it.
Dear Anil,
I agree with my colleague Ravinder. I have followed the same protocol. Glycerol stock media ( store at -20C for few months or at -80C for decades).
Good Luck!
Could any one explain is there any medium for bacteria on which CFU will remain same up to 6 month and more at room temperature, glycerol stock needs -20 o C
lyophilization is also a method to preserve but I do not know about CFU will remain same.
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