Reactivation of the endospore occurs when conditions are more favourable and involves activation, germination, and outgrowth. Prolonged exposure to ionising radiation, such as x-rays and gamma rays, will also kill most endospores. It was the usual method for a while in the late 19 th century before the advent of inexpensive autoclaves. This indirect method is called Tyndallization. They will germinate within a day or two with the right environmental conditions, and then the vegetative cells can be straightforwardly destroyed. An indirect way to destroy them is to place them in an environment that reactivates them to their vegetative state. Endospores are able to survive boiling at 100☌ for hours, although the longer the number of hours the fewer that will survive. While resistant to extreme heat and radiation, endospores can be destroyed by burning or by autoclaving. Sporulation is now complete, and the mature endospore will be released when the surrounding vegetative cell is degraded. 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 unfavorable it may start the process of endosporulation, which takes about eight hours. Figure: Bacillus subtilis stained with the Schaeffer-Fulton stain.: A stained preparation of Bacillus subtilis showing endospores as green and the vegetative cell as red. Sometimes the endospore can be so large that the cell can be distended around the endospore. Bacteria having a centrally placed endospore include Bacillus cereus, and those having a subterminal endospore include Bacillus subtilis. Examples of bacteria having terminal endospores include Clostridium tetani, the pathogen that causes the disease tetanus. There are variations in endospore morphology. Another staining technique for endospores is the Schaeffer-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 colorless. Viewing endospores under the light microscope can be difficult due to the impermeability of the endospore wall to dyes and stains. Figure: Endospore morphology: Variations in endospore morphology: (1, 4) central endospore (2, 3, 5) terminal endospore (6) lateral endospore. Bacteria produce a single endospore internally. They are commonly found in soil and water, where they may survive for long periods of time. They are resistant to ultraviolet radiation, desiccation, high temperature, extreme freezing and chemical disinfectants. Endospores can survive without nutrients. The endospore consists of the bacterium’s DNA and part of its cytoplasm, surrounded by a very tough outer coating. Examples of bacteria that can form endospores include Bacillus and Clostridium. When the environment becomes more favorable, the endospore can reactivate itself to the vegetative state. Endospores enable bacteria to lie dormant for extended periods, even centuries. In endospore formation, the bacterium divides within its cell wall. Endospore formation is usually triggered by lack of nutrients, and usually occurs in Gram-positive bacteria. \)ĭescribe the function and advantage of endospore formation, as well as the methods for viewing it.Īn endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria from the Firmicute phylum.
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