Freezing Selects for Phage T7 Deletion Mutations… Not!

Stephen T. Abedon

Department of Microbiology – The Ohio State University – –


Myth: Freezing phage T7 can select for deletion mutations…

From Clark and Geary (1973), with emphasis added:

ATCC freeze-dries phages for distribution (Clark and Geary, 1969). Davis and Hyman (1971) have reported the existence of at least two authentically different T7 phage strains, T7M (Meselsohn) and T7L (Luria) (ATCC 11303-B7). They also stated that T7L lyophilized stock from ATCC contained a high percentage of deletions in the DNA molecule, and they attributed this to lyophilization selecting for DNA deletions. However, since this publication, ATCC prevailed upon these authors to test the ATCC broth stock of T7L, which had been maintained at 4° C unlyophilized or unfrozen since its deposit in the Collection by Luria in 1952. They reported in a letter to W. A. Clark that the T7L stock before freeze-drying contained the same deletions as the freeze-dried product.

In other words, the evidence is not consistent with freezing selecting for deletion mutations in phage T7…


Clark, W. A., and D. Geary. 1969. The collection of bacteriophages at the American Type Culture Collection, p. 179-187. In T. Nei (ed.), Freezing and Drying Microorganisms. University Park Press, Baltimore.

Clark, W. A., and D. Geary. 1973. Preservation of bacteriophages by freezing and freeze-drying. Cryobiology 10:351-360.

Davis, R. W., and R. W. Hyman. 1971. A study of evolution: The DNA base sequence homology between coliphages T3 and T7. J. Mol. Biol. 62:287-301.