Fig. 1.

Morphological changes and compartment specific σ-factors during B. subtilis endospore formation.

(i) The polar septum forms with a thick layer of PG separating the mother cell and the forespore. PG is indicated in light grey. σ^F becomes active in the forespore and initiates a signalling pathway that leads to activation of σ^E in the mother cell.

(ii) The septal PG is thinned.

(iii) During engulfment, the forespore is released from the cell wall by PG hydrolysis and the mother cell membrane migrates in the wake of the hydrolysed PG.

(iv) σ^G becomes active in the developing spore after completion of engulfment and initiates a signalling pathway that leads to activation of σ^K in the mother cell.

(v) Cortex forms between the inner and outer spore membranes and coat proteins (dark grey) assemble on the spore surface. The mother cell lyses and the mature endospore is released.