endospora

Endospora, commonly referred to as endospore, is a dormant, highly resistant intracellular structure produced by certain gram-positive bacteria in response to nutrient limitation. Endospores enable survival through extreme environmental stresses and can remain viable for long periods. In favorable conditions, an endospore can germinate and return to a metabolically active vegetative cell.

Endospore formation, or sporulation, is a regulated developmental process initiated by a rise in the intracellular signal Spo0A. It involves asymmetric cell division that produces a smaller forespore inside a larger mother cell. The mature endospore is released when the mother cell lyses. The spore is protected by layers: the cortex of specialized peptidoglycan, a proteinaceous coat, and sometimes an outer exosporium.

Within the core, DNA, ribosomes, and essential enzymes are kept in a highly desiccated, metabolically inert state. Calcium-dipicolinate, low water content, and small acid-soluble proteins stabilize the genome and contribute to heat and chemical resistance. SASPs also bind and protect DNA from damage and contribute to UV resistance.

Endospores are formed by many Bacillus and Clostridium species. Their resilience complicates sterilization in medicine and food processing, as standard disinfection may fail. Effective sterilization typically requires high-temperature moist heat (autoclaving) or validated sporicidal procedures. Endospore formation thus has important implications for infection control, food safety, and environmental microbiology.