page_title: Endospore
section_title: Structure
hierarchical_section_title: Endospore / Structure
caption_attribution_description: Čeština: Různé druhy bakteriálních spor podle umístění v rámci mateřské buňky. Deutsch: Form und Lage von Endosporen bei verschiedenen Bakterien: 1. Spore zentral 2. Spore terminal mit Einschlusskörper (Protein) 3. Spore terminal, Bakterie keulenförmig aufgetrieben 4. Spore zentral, Bakterie spindelförmig aufgetrieben ("Clostridium-Form") 5. Spore terminal, rund = Plectridium 6. Spore lateral, Bakterie spindelförmig aufgetrieben. Sporenformen von Bacillus. English: Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore. Íslenska: Nokkrar formgerðir dvalargróa og staðsetning þeirra í frumunni: (1, 4) miðlæg gró; (2, 3, 5) endastæð gró; (6) hliðlæg gró. Nederlands: Variatie in de morfologie van endosporen. 1. Centrale spore 2. Terminale spore met insluitingsdeeltje (Proteïne) 3. Terminale spore, waarbij de bacterie knotsvormig is uitgestulpt 4. Centrale spore, waarbij de bacterie spoelvormig is uitgestulpt ("Clostridium-vorm") 5. Terminale spore, rond = Plectridium 6. Laterale spore, waarbij de bacterie naar een kant spoelvormig is uitgestulpt. Português: Variação na morfologia dos endosporos. (1, 4) Endosporo central, (2, 3, 5) Endosporo terminal, (6) Endosporo lateral. Русский: Расположение эндоспор: 1, 4 — центральное, 2, 3, 5 — терминальное, 6 — латеральное. Українська: Типи морфології ендоспор. (1, 4) Центральна ендоспора, (2, 3, 5) термінальна ендоспора, (6) бічна ендоспора. Варіації морфологфї ендоспор. (1, 4) Центральна, (2, 3, 5) термінальна, (6) бічна. 中文: 芽孢的變異形態。 (1, 4) Central endospore, (2, 3, 5) terminal endospore, (6) lateral endospore.
context_page_description: An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Firmicutes. The name "endospore" is suggestive of a spore or seed-like form, but it is not a true spore. It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other. Endospores enable bacteria to lie dormant for extended periods, even centuries. There are many reports of spores remaining viable over 10,000 years, and revival of spores millions of years old has been claimed. There is one report of viable spores of Bacillus marismortui in salt crystals approximately 250 million years old. When the environment becomes more favorable, the endospore can reactivate itself to the vegetative state. Most types of bacteria cannot change to the endospore form. Examples of bacterial species that can form endospores include Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, and Clostridium tetani.
context_section_description: Bacteria produce a single endospore internally. The spore is sometimes surrounded by a thin covering known as the exosporium, which overlies the spore coat. The spore coat, which acts like a sieve that excludes large toxic molecules like lysozyme, is resistant to many toxic molecules and may also contain enzymes that are involved in germination. In Bacillus subtilus endospores, the spore coat is estimated to contain more than 70 coat proteins, which are organized into an inner and an outer coat layer. The X-ray diffraction pattern of purified B. subtilis endospores indicates the presence of a component with a regular periodic structure, which Kadota and Iijima speculated might be formed from a keratin-like protein. However, after further studies this group concluded that the structure of the spore coat protein was different from keratin. When the B. subtilis genome was sequenced, no ortholog of human keratin was detected. The cortex lies beneath the spore coat and consists of peptidoglycan. The core wall lies beneath the cortex and surrounds the protoplast or core of the endospore. The core contains the spore chromosomal DNA which is encased in chromatin-like proteins known as SASPs (small acid-soluble spore proteins), that protect the spore DNA from UV radiation and heat.  The core also contains normal cell structures, such as ribosomes and other enzymes, but is not metabolically active.
  Up to 20% of the dry weight of the endospore consists of calcium dipicolinate within the core, which is thought to stabilize the DNA. Dipicolinic acid could be responsible for the heat resistance of the spore, and calcium may aid in resistance to heat and oxidizing agents. However, mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are also at work. Small acid-soluble proteins (SASPs) are found in endospores. These proteins tightly bind and condense the DNA, and are in part responsible for resistance to UV light and DNA-damaging chemicals.
  Visualising endospores under light microscopy can be difficult due to the impermeability of the endospore wall to dyes and stains. While the rest of a bacterial cell may stain, the endospore is left colourless. To combat this, a special stain technique called a Moeller stain is used. That allows the endospore to show up as red, while the rest of the cell stains blue. Another staining technique for endospores is the Schaeffer-Fulton stain, which stains endospores green and bacterial bodies red. The arrangement of spore layers is as follows:
  Exosporium
  Spore coat
  Spore cortex
  Core wall
caption: Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore
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