Conditional temperature-sensitive restriction of Pseudomonas bacteriophge CB3.

Restriction of Pseudomonas bacteriophage CB3 growth on some Pseudomonas aeruginosa hosts was studied. On restricting hosts, growth of this phage was severely inhibited below 32 C and hence was temperature-sensitive. Investigation of this phenomenon revealed that restricting hosts were not killed as a consequence of their infection under nonpermissive conditions. The ability of some hosts to restrict showed segregation in sexual crosses between restricting and nonrestricting hosts. However, the pattern of restriction among various hosts differed with the phage in question when other phages were compared with CB3. Temperature-shift experiments indicated that blockage of an early event in the phage lytic cycle occurred when restricting conditions were imposed on cells infected with CB3. This blockage could be eliminated by holding at permissive conditions until the cold-sensitive step was bypassed or by pulsing restricting cells for 5 min at 37 C.