TEMPERATURE-SENSTIVIE MUTANTS OF BACILLUS SUBTILIS BACTERIOPHAGE SP3. I. ISOLATION AND CHARACTERIZATION.

Nishihara, Mutsuko (University of California, Los Angeles), and W. R. Romig. Temperature-sensitive mutants of Bacillus subtilis bacteriophage SP3. I. Isolation and characterization. J. Bacteriol. 88:1220-1229. 1964.-Twelve temperature-sensitive mutants of Bacillus subtilis bacteriophage SP3 were isolated from a suspension of the wild type treated with nitrous acid. The mutants were detected because of an impaired ability to replicate in the host cell at 45 C, in contrast to the parental wild type which has essentially the same burst size at temperatures between 37 and 48 C. However, the latent period of the wild-type phages was decreased as growth temperatures were varied from 37 to 49 C. The reduction of burst size at temperatures above 48 C is probably the result of the effect of higher temperatures on the metabolism of the host, because the bacterial growth rate is decreased between 45 and 51 C. A temperature effect on the mutants was studied by infecting cells at 45 C, and then transferring portions of the mixture to 37 C at two time intervals. One transfer was made within the expected 45 C latent period, and the other was made about 10 min after the end of the latent period. In both cases, removal of the phage-bacterium complexes from the inhibitory condition of high temperature did not result in an immediate increase of plaque-forming units. A delay was observed which might correspond to the time necessary to complete the temperature-sensitive synthesis in the infected cells. In experiments with three of the mutants, cells infected at 37 C were transferred to 45 C at various times during the 37 C latent period. The extent of inhibition upon transfer to the high temperature was found to decrease progressively with increasing time of prior incubation at 37 C.