Entry into sporulation only occurs at a specific time during the cell cycle, when the cell harbors exactly two replicated chromosomes but has not initiated a further round of DNA replication.

Why would a cell Sporulate?

Essentially, sporulation refers to the formation of spores from vegetative cells during unfavorable environmental conditions. As such, it may be described as an adaptive response that allows the organism to survive given adverse conditions (radiation, extreme heat or cold, lack of nutrition etc).

What causes bacteria to sporulate?

Sporulation is a drastic response undertaken by some bacteria, mostly Firmicutes, in response to extreme stress. During sporulation, the growing cell (also referred to as a vegetative cell) will forego normal cellular division to instead form an endospore.