A REVERSIBLE TRANSFORMATION OF T1 BACTERIOPHAGE

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Abstract
In dist. water or dilute phosphate buffer, Tl bacteriophage undergoes a transformation to a sensitized form that loses its ability to form plaques if it is immediately added to a suspension of host cells in broth. This transformation can be reversed by allowing such sensitized phage to recover in plain broth before the addition of the cells, in which case almost the theoretical number of plaques is obtained when the mixture is plated. Sensitization could be prevented by CaCl2 in the equilibration medium in a concn. of 10-4 [image] or higher. Inactivation of sensitized phage involves direct interaction with host cells and only occurs under conditions that allow adsorption of the phage. The rate of this inactivation is the same as the rate of adsorption of normal phage. It is concluded that sensitization produces a block in some step of the virus metabolic cycle occurring after adsorption. The act of adsorption renders this transformation irreversible causing loss of the virus activity. The adsorption constant for Tl phage on Escherichia coli B in broth at 15[degree]C is 2.7 x 10-10 cm3 minutes1. The strain of T1 phage employed is not adsorbed on host cells in dist. water at 15[degree]C. Adsorption does take place in a solution of glucose and inorganic salts, and the rate is exactly the same as in broth at the same temp. The significance of the ability of bacteriophage to undergo reversible transformations to forms with different metabolic properties is discussed.