Endosporen

Endosporen, or endospores, are dormant, highly resistant structures formed by certain Gram-positive bacteria, most notably Bacillus and Clostridium species. They enable survival under harsh environmental stresses such as extreme heat, desiccation, radiation, and chemical disinfectants. Endosporen are not reproductive cells but long-term survival forms that can persist for years or longer in a wide range of habitats.

An endospore consists of a central core containing DNA, RNA, and ribosomes; a thick cortex made of peptidoglycan; and multiple protein layers including the spore coat and, in many species, an outer layer called the exosporium. The core is dehydrated and enriched with dipicolinic acid and small acid-soluble proteins that help stabilize DNA and other vital macromolecules.

Sporulation is triggered by nutrient limitation and proceeds via an asymmetric cell division that forms a forespore within the mother cell. Through a series of sigma-factor–driven stages, the forespore is engulfed, matures, and is eventually released as a mature endospore upon lysis of the mother cell. In favorable conditions, endospores germinate, rehydrating and shedding protective layers to resume metabolic activity and growth as vegetative cells.

Endospores have significant practical implications. They contribute to the persistence and transmission of pathogens such as Bacillus anthracis and Clostridium botulinum and pose challenges for food safety and clinical decontamination. They are also used as biological indicators in sterilization validation. Effective control requires methods such as moist-heat sterilization (autoclaving), chemical sporicides, or irradiation.