Protein-coated vesicles are ubiquitous in nature and include the clatherin-coated vesicles that mediate endocytosis in eukaryotes. In response to starvation in Bacillus subtilis the genome is replicated and stored in a dehydrated, dormant and durable protein-coated vesicle called the spore. The proteinaceous spore coat is the outer interface of the spore with the environment and provides physical integrity by protecting from predatory protists during dormancy. Dormancy is broken by germination, which is triggered by the interaction of signals from the surrounding environment with receptors located underneath the spore coat. During germination the spore cracks open and a new vegetative cell grows out. Thus, the spore coat must be permeable as well as protective.

In this work we have examined the assembly and organization of the spore coat. We measured the localization of spore coat proteins at high resolution and found evidence for four distinct spore coat layers and characterized a previously uncharacterized outermost layer that we named the crust. We also examined the dynamics of localization of individual spore coat proteins in live cells. We describe a model of spore coat morphogenesis in which a spatially organized scaffold of the four coat layers is assembled as a cap on one pole of the developing spore. This is followed by multiple distinct waves of a process that we previously named encasement, which completes the formation of a full shell of protein around the circumference of the spore. We conclude with a quantitative reexamination of the phenotypes of mutants of genes required for assembly of the spore coat, the morphogenetic proteins.