Lysogenic induction ends the stable association between a bacteriophage and its host, and
the transition to the lytic cycle begins with early prophage excision followed by DNA replication and packaging (ERP). This temporal program is considered universal for P22-like
temperate phages, though there is no direct evidence to support the timing and sequence of
these events. Here we report that the long-standing ERP program is an observation of the
experimentally favored Salmonella phage P22 tsc229 heat-inducible mutant, and that wildtype P22 actually follows the replication-packaging-excision (RPE) program. We find that P22
tsc229 excises early after induction, but P22 delays excision to just before it is detrimental to
phage production. This allows P22 to engage in lateral transduction. Thus, at minimal
expense to itself, P22 has tuned the timing of excision to balance propagation with lateral
transduction, powering the evolution of its host through gene transfer in the interest of selfpreservation.