A specific reversible inhibition of bacteriophage T2.

With most phages, the titer of a lysate measured by plaque count remains stable from the time of lysis or shows a progressive decrease as phage becomes inactivated by a variety of environmental agents. Freshly prepared lysates of bacteriophage T2 of Escherichia coli rise in titer spontaneously with time, the maxmum titer being reached in several weeks under refrigeration. Bertani (unpublished data, 1950) noted that this rise could be accelerated greatly by diluting a lysate in distilled water or by adding ZnSO4 to a final concentration of one per cent. Watson (personal communication, 1951) observed that lysates of T2 to which antibacterial serum was added before lysis did not show any rise in titer after dilution in distilled water. This suggested that normal lysates contained a certain proportion of particles that are prevented from forming plaques because of combination with specific host materials. The present paper provides evidence of the occurrence of such combination and of the properties of the combined phage.