sporecoat

Spore coat is the multilayer protein shell that surrounds the spore core of bacterial endospores, notably in Gram-positive genera such as Bacillus and Clostridium. It forms during sporulation when a developing forespore is engulfed by the mother cell and becomes enveloped by multiple coat layers. The coat is typically described as having an inner coat and an outer coat, composed of a diverse set of coat proteins that assemble around the forespore.

Biogenesis of the spore coat is tightly regulated. A cascade of sporulation-specific sigma factors controls the temporal expression of coat protein genes, while morphogenetic proteins guide the proper localization and assembly of the coat around the forespore. This coordinated process results in a durable protective shell that is relatively impermeable to many environmental stresses.

Composition and properties of the coat contribute to the spore’s resistance. The coat, together with the cortex and spore core, provides protection against heat, desiccation, UV radiation, chemical disinfectants, and enzymatic degradation. The exact protein composition varies by species, and the outer coat often contains proteins that influence permeability and environmental interactions.

Function and significance. The spore coat is central to the survival of endospores in hostile conditions and plays a role in the timing of germination when favorable conditions return. Endospores are notable for their environmental persistence, which has implications for food safety, infection control, and microbial ecology. In biotechnology, spore coats have been explored as display platforms for antigens in vaccine development, leveraging the robustness of spores for oral delivery.