Bacterial spores

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Bacterial spores:

Bacterial spores Dr.k.s.kumudhavalli

Whats an endospore? :

Whats an endospore ? dormant , tough, and non-reproductive structure produced by certain bacteria when the bacterium is experiencing an environment that is deleterious to the usual vegetative state of the bacterium, notably including when the bacterium is getting dried out (desiccated). survival of a bacterium through periods of environmental stress. consists of the bacterium's DNA and part of its cytoplasm, surrounded by a very tough outer coating.

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Endospores can survive without nutrients. They are resistant to ultraviolet radiation, desiccation, high temperature, and chemical disinfectants. Some classes of bacteria can turn into exospores, a.k.a. microbial cysts , instead of endospores . Exospores and endospores are two kinds of "hibernating“ stages seen in some classes of microorganisms.




location The position of the endospore differs among bacterial species and is useful in identification. The main types within the cell are terminal, subterminal , and centrally placed endospores . Terminal endospores are seen at the poles of cells, whereas central endospores are more or less in the middle. Subterminal endospores are those between these two extremes, usually seen far enough towards the poles but close enough to the center so as not to be considered either terminal or central. Lateral endospores are seen occasionally

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Variations in endospore morphology: (1, 4) central endospore ; (2, 3, 5) terminal endospore ; (6) lateral endospore


visualization Visualising spores through light microscope can be difficult due to the impermeability of the endospore wall to dyes and stains. special stain technique Moeller stain the Schaeffer-Fulton stain , The arrangement of spore layers is as follows: Exosporium Spore coat Spore cortex Core wall


formation bacteria based on nutrients If available if not available Undergo binary fission DNA condenses spore formation occurs

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DNA divides into 2 complete copies. The mother cell membrane invaginates to form the developing forespore . The mother cell membrane continues to grow and engulfs the developing spore developing spore is surrounded by 2 layers Peptidoglycan is laid between 2 layers of developing spore to form cortex Dipicolinic acid is formed inside and Ca++ enters from outside . As Ca++ enters the spore water is removed

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Protein coat is formed exterior to cortex Spore becomes mature Mature spore is resistant to environmental conditions Some spore form additional layer called EXOSPORIUM Finally, lytic enzymes destroy the mother cell. The mature spore is released.

Spore cycle:

Spore cycle DNA condenses mother cell membrane invaginates forespore . cortex Mature spore


destruction While resistant to extreme heat and radiation, endospores can be destroyed by burning or by autoclaving . Endospores are able to survive boiling at 100°C for hours, although the longer the number of hours the fewer that will survive. Tyndallization An indirect way to destroy them is to place them in an environment that reactivates them to their vegetative state. They will germinate within a day or two with the right environmental conditions, and then the vegetative cells can be straightforwardly destroyed. Prolonged exposure to high energy radiation, such as x-rays and gamma rays , will also kill most endospores .

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sterilization control dry heat moist heat Spores of non spores of bacillus - toxigenic strains of stereothermophilus Cl.tetani


reactivation Reactivation of the endospore occurs when conditions are more favourable . involves Activation Germination outgrowth


activation Activation may be triggered by heating the endospore


germination germination involves the dormant endospore starting metabolic activity and thus breaking hibernation. It is commonly characterised by rupture or absorption of the spore coat, swelling of the endospore , an increase in metabolic activity, and loss of resistance to environmental stress


outgrowth Outgrowth follows germination. It involves the core of the endospore manufacturing new chemical components and exiting the old spore coat to develop into a fully functional vegetative bacterial cell, which can divide to produce more cells.

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