endospores

Endospores are highly durable, dormant cell forms produced by certain Gram-positive bacteria, most notably in the genera Bacillus and Clostridium. They form within a mother cell when the environment becomes unfavorable, such as during nutrient limitation, to ensure the survival of the genetic material and associated enzymes during harsh conditions.

The spore consists of a core that contains DNA and ribosomes, surrounded by protective layers including a cortex of peptidoglycan and a protein-rich spore coat. The core has very low water content and high levels of dipicolinic acid and calcium, which help stabilize proteins and nucleic acids, contributing to resistance to heat, desiccation, radiation, and many chemicals.

Sporulation is a developmental program that culminates in the release of a mature endospore from the mother cell. Endospores are metabolically inactive, highly resistant, and capable of persisting in soil, dust, and clinical environments for long periods. Germination occurs when conditions improve and nutrients become available; the endospore rehydrates, resumes metabolism, and returns to a vegetative cell that can grow and divide.

Ecology and significance: Endospore-forming bacteria are common in soil and aquatic habitats. Some species are notable pathogens, such as Bacillus anthracis and Clostridium botulinum, C. tetani, and C. difficile, which produce toxins. Others, including Bacillus subtilis, have important roles in industry and research. Because spores resist many disinfection methods, proper sterilization, often involving high heat and pressure, is essential in healthcare, food processing, and laboratory settings.

Comparison with vegetative cells: Endospores are dormant and non-reproductive survival structures, whereas vegetative cells are metabolically active and capable of growth and division.