The Bacillus spore coat

Bacilli, which are abundant in the soil, form highly resistant dormant cell types, called spores, in response to starvation. The spore is organized into a series of concentrically arranged structures, each of which contribute in a different way to resistance against environmental stress. In certain bacteria, including Bacillus subtilis, the outermost of these structures is a multilayered protein shell, called the coat. The coat is both an armor plating and, almost certainly, possesses enzymatic activities, allowing it to have active roles as well. Assembly of the proteins comprising the coat is carefully controlled during spore assembly, resulting in a distinct pattern of layers, seen in cross section, and a discreet pattern of ridges on the surface. Although our understanding of spore coat composition and assembly is deepening, we still know little about the roles of the coat in interactions between spores and other organisms, particularly in the soil. Critical future directions for spore coat research include continued identification of the proteins that comprise the coat surface, characterization of the global chemical characteristics of this surface, and elucidation of how these features impact on other organisms in the soil.