Figure 1.

Schematic diagram of the engulfment complex. (A) A sporangium during the morphological processes of engulfment. The membranes of the mother cell (purple) are migrating around the forespore (blue). The cell wall PG encasing the two cells is in green. IID (D), IIP (P), and IIM (M) are all made in the mother cell and localize to the leading edge of the engulfing septal membrane. IID (D) and IIP (P) both have a single N-terminal transmembrane segment and a large extracellular domain. IIM (M) is predicted to have five transmembrane segments. Genetic, biochemical, and cytological analysis indicate that these three proteins reside in a membrane complex (Aung et al. 2007; Chastanet and Losick 2007). (B) Schematic diagram of the PG meshwork. Glycan chains (hexagons) composed of GlcNAc (G) and MurNAc (M) are linked by glycosidic bonds. Attached to the MurNAc (M) sugars are short peptides (balls) that cross-link adjacent glycan strands, generating a continuous 3D meshwork that envelops the bacterium. Gram-positive bacteria like B. subtilis have multiple layers of PG.