![]() ![]() Reactivation of the endospore occurs when conditions are more favourable and involves activation, germination, and outgrowth. Prolonged exposure to high energy radiation, such as xrays and gamma rays, will also kill most endospores. Exposure to extreme heat for a long enough period will generally have some effect, though many endospores can survive hours of boiling or cooking. ![]() Whilst resistant to extreme heat and radiation, endospores can be destroyed by burning or autoclaving. Alkylating agents however, such as ethylene oxide, are effective against endospores. Household cleaning products generally have no effect, nor do most alcohols, quaternary ammonium compounds or detergents. Sporulation is now complete, and the mature endospore will be released when the surrounding vegetative cell is degraded.Įndospores are resistant to most agents which would normally kill the vegetative cells they formed from. Next the peptidoglycan cortex forms between the two layers and the bacterium adds a spore coat to the outside of the forespore. Calcium dipicolinate is incorporated into the forespore during this time. The plasma membrane of the cell surrounds this wall and pinches off to leave a double membrane around the DNA, and the developing structure is now known as a forespore. The DNA is replicated and a membrane wall known as a spore septum begins to form between it and the rest of the cell. When a bacterium detects environmental conditions are becoming unfavourable it may start the process of sporulation, which takes about eight hours. Another staining technique for endospores is the Schaffer-Fulton stain, which stains endospores green and bacterial bodies red. That allows the endospore to show up as red, while the rest of the cell stains blue. To combat this, a special stain technique called a Moeller stain is used. While the rest of a bacterial cell may stain, the endospore is left colourless. Visualising endospores under the light microscope can be difficult due to the impermeability of the endospore wall to dyes and stains. Sometimes the endospore can be so large the cell can be distended around the endospore, this is typical of Clostridium tetani. Bacteria having a centrally placed endospore include Bacillus cereus, and those having a subterminal endospore include Bacillus subtilis. Lateral endospores are seen occasionally.Įxamples of bacteria having terminal endospores include Clostridium tetani, the pathogen which causes the disease tetanus. 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. Terminal endospores are seen at the poles of cells, whereas central endospores are more or less in the middle. The main types within the cell are terminal, subterminal and centrally placed endospores. The position of the endospore differs among bacterial species and is useful in identification. However, mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work. Dipicolinic acid could be responsible for the heat resistance of the spore, and calcium may aid in resistance to heat and oxidizing agents. Up to 15% of the dry weight of the endospore consists of calcium dipicolinate within the core, which is thought to stabilize the DNA. The core has normal cell structures, such as DNA and ribosomes, but is metabolically inactive. The core wall lies beneath the cortex and surrounds the protoplast or core of the endospore. The cortex lies beneath the spore coat and consists of peptidoglycan. The spore coat is impermeable to many toxic molecules and may also contain enzymes that are involved in germination. The spore is often surrounded by a thin covering known as the exosporium, which overlies the spore coat. In contrast to eukaryotic spores, which are produced by many eukaryotes for reproductive purposes, bacteria will produce a single endospore internally. ![]()
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