Experiments on the inactivation of bacteriophage by radiations, and their bearing on the nature of bacteriophage

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Abstract
Phages S-13 (active against Shigella dysenteriae Y6R), C-36 (active against Escherichia coli), and Staph-K (active against Staphylococcus S 3K) were dried on gelatin coated cover-slips and exposed to measured amts. of x-rays of radium (I), x-rays of wave-length 1.5 A (II), 4eMV x-rays of polonium (III), 7eMV x-rays of RaC1 (IV), and screened x-rays of RaC1 averaging 4eMV (V). Survival of phage was detd. by plaque-counting technique on agar plates. Straight lines are obtained by plotting the logarithm of the fraction surviving against dose of radiation. The effect of a given dose was independent of the exposure time. Inactivation dose (i.d.) is defined as the dose of radiation which reduces the natural logarithm of surviving activity to[long dash]1 (ratio of exptl. to control plaque count is 0.37). I.d.''s in millions of roentgens are: for S-13, (I) 0.58, (II) 0.99, (III) 3.5; for C-36, (I) 0.21, (II) 0.43, (III) 0.94; for Staph-K, (I) 0.079, (II) 0.109, (III) 0.45, (IV) 0.21, (V) 0.59. Assuming that a single atomic ionization in the radiosensitive area inactivates phage, S-13 is a macromolecular type of virus with radiosensitive area identical with particle area. C-36 and Staph-K, with radiosensitive area (gene area) less than particle area, are considered as elementary organisms. The data conform to the concept that C-36 contains 9 genes of 10 m.fx diameter and Staph-K contains 14 genes of 12.5 mju diameter.