My lab doesn't use phage often and recently ran into a problem with too-low of titer for our phi 11 (to the point where I couldn't get it to lyse after 3 and 24 hours). We make a lysate prep, filter sterilize and store in -20. Is there a better way to store this, and/or are we just not using it enough? Should we try to maintain our phage every couple months so we don't run into this problem?
All phage are different when it comes to stability and storage condition. I've had some phages that the titer didn't change over a period of a few years, and others that went down quickly in months. Usually I stored phages at refrigerator (4oC) temp.
I imagine that repeated freeze thaw cycles are probably not good for a phage stock. So first of all is your -20 freezer a no-frost freezer? If so, then you are probably subjecting the phage to freeze thaw cycle every day. You can get around this if this phage stock is in a container stored by a freezer brick so that the local temp of the tube doesn't go above freezing.
You could try making a fresh stock from a single plaque and then make lots of aliquots so that you take one out each time you need it. I would test whether it is more stable at -20 or -80 or 4. Give it month and then do spot titers to see what is best.
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