Final answer:
The excision from lysogenic lifestyle to lytic lifestyle occurs when environmental stress factors precipitate the excision of prophage DNA from the bacterial host's chromosome, leading to the initiation of the lytic cycle.
Step-by-step explanation:
Excision from lysogenic lifestyle to lytic lifestyle occurs when the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle. This event is often triggered by environmental stress factors such as UV light or exposure to toxic chemicals. During the lysogenic cycle, the phage DNA is integrated into the host bacteria's genome and can be replicated along with it. However, when the host cell is threatened, the phage can switch to the lytic cycle, where it replicates independently, causing the breakdown of the host cell and the release of new viral particles.