FIG. 1.

Engulfment in B. subtilis. (A) Asymmetric division produces the small forespore and large mother cell. Septal thinning (step i) commences at the septal midpoint and proceeds towards the edges, followed by membrane migration up (step ii) and around (step iii) the forespore, until the membrane meets and fuses (step iv) to release the forespore into the mother cell cytoplasm. (B) In the absence of SpoIID, SpoIIM, or SpoIIP, septal thinning is blocked, and the forespore ultimately bulges into the mother cell. (C) In the absence of SpoIIB, septal thinning is slowly and uneven, forming a transient bulge, although engulfment is ultimately completed. In the absence of both SpoIIB and SpoVG, membrane migration is blocked.