The linear double-stranded DNA of phage Bam35 enters lysogenic host cells, but the late phage functions are suppressed

Bam35, a temperate double-stranded DNA bacteriophage with a 15-kb linear genome, infects gram-positive Bacillus thuringiensis cells. Bam35 morphology and genome organization resemble those of PRD1, a lytic phage infecting gram-negative bacteria. Bam35 and PRD1 have an outer protein coat surrounding a membrane that encloses the viral DNA. We used electrochemical methods to investigate physiological changes of the lysogenic and nonlysogenic hosts during Bam35 DNA entry and host cell lysis. During viral DNA entry, there was an early temporal decrease of membrane voltage associated with K+ efflux that took place when either lysogenic or nonlysogenic hosts were infected. Approximately 40 min postinfection, a second strong K+ efflux was registered that was proposed to be associated with the insertion of holin molecules into the plasma membrane. This phenomenon occurred only when nonlysogenic cells were infected. Lysogenic hosts rarely were observed entering the lytic cycle as demonstrated by thin-section electron microscopy.