Effect of Urea upon Activity of Bacteriophage. ∗

Abstract

In attempting to minimize denaturation of phage by heat we employed a number of substances which various investigators have found to prevent denaturation of proteins. 1 While some of these substances delayed denaturation of phage (saccharose, glycerine and to lesser extent CaCl₂ or glucose) other substances (sodium salicylate, Bayer 205, or urea) exhibited no gross protective effect. During these experiments it was noted, however, that when mixtures containing phage and urea were plated with homologous bacteria at intervals during the experiment (before the inactivation of phage has occurred) the plaques of lysis appeared to be larger and noticeably clearer than on control plates containing the phage without the addition of urea. This apparent intensification of lysis in the presence of urea suggested the possibility that addition of urea may perhaps bring out the lytic activity of phage under circumstances where lysis is ordinarily inhibited, as for instance on 4% agar. As we have shown, under these circumstances bacteria failed to undergo lysis, although the phage effect is not entirely abolished, as evidenced by the increase in the rate of multiplication of bacteria in contact with it. 2 We were interested in determining whether the addition of urea to the medium would promote lysis under these circumstances.

To measured amounts of a suspension of bacteria (growth from 10 agar slants of an 18 hour culture suspended in 40 cc. of broth) were added different amounts of a sterile (filtered) 50% solution of urea as shown in the protocol; 1.5 cc. of the respective mixtures were added each to 10 cc. of molten agar of different concentrations, and after thorough mixing poured into Petri plates, each mixture was made in duplicate.