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It is larger than lipid inclusion granules and is often ovoid, in contrast to the spherical shape of the lipid granules. In unstained preparations the spore is recognised within the parent cell by its greater refractility.
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The end result is a morphologically distinct structure, the endospore, within the mother cell. In the face of sporulation stimuli, classically starvation or transition from growth to stationary phase, a programme of sequential expression of specific genes is triggered. Geneticists have viewed sporulation as a paradigm of a simple differentiation process, and the key molecular processes required in Bacillus subtilis are now understood in detail. The process does not involve multiplication: in sporulation, each vegetative cell forms only one spore, and in subsequent germination, each spore gives rise to a single vegetative cell. Some bacteria, notably those of the genera Bacillus and Clostridium, develop a highly resistant resting phase or endospore, whereby the organism can survive in a dormant state through a long period of starvation or other adverse environmental conditions (resuscitation of spores several thousand years old has been claimed). Barer undefined, in Medical Microbiology: A Guide to Microbial Infections, 2019 Bacterial spores Once germination has begun and the spore coat has been compromised, the spore is weakened and vulnerable, and can be inactivated like other bacteria. After the germination process begins, the spore will take up water, swell, shed its coats, and produce one new vegetative cell identical to the original vegetative cell, completing the entire cycle. The process takes approximately 90 minutes. Germination of spores into the vegetative state is stimulated by disruption of the outer coat by mechanical stress, pH, heat, or another stressor and requires water and a triggering nutrient (e.g., alanine). The process requires 6 to 8 hours for completion. The cortex is surrounded by the tough keratin-like protein coat that protects the spore. These two layers are surrounded by the cortex, which is made up of a thin inner layer of tightly cross-linked peptidoglycan surrounding a membrane (which used to be the cytoplasmic membrane) and a loose outer peptidoglycan layer. This wraps the DNA in the two layers of membrane and peptidoglycan that would normally divide the cell. After duplication of the chromosome, one copy of the DNA and cytoplasmic contents (core) are surrounded by the cytoplasmic membrane, the peptidoglycan, and the membrane of the septum. Dipicolinic acid is produced, and antibiotics and toxins are often excreted. Spore mRNAs are transcribed, and other mRNAs are turned off. Spores also are difficult to decontaminate with standard disinfectants or autoclaving conditions.ĭepletion of specific nutrients (e.g., alanine) from the growth medium triggers a cascade of genetic events (comparable to differentiation) leading to the production of a spore. In fact, bacterial spores are so resistant to environmental factors that they can exist for centuries as viable spores. The structure of the spore protects the genomic DNA from intense heat, radiation, and attack by most enzymes and chemical agents. The spore looks refractile (bright) in the microscope. The spore has an inner membrane, two peptidoglycan layers, and an outer keratin–like protein coat. It contains a complete copy of the chromosome, the bare minimum concentrations of essential proteins and ribosomes, and a high concentration of calcium bound to dipicolinic acid. The spore is a dehydrated multishelled structure that protects and allows the bacteria to exist in “suspended animation” ( Fig. The location of the spore within a cell is a characteristic of the bacteria and can assist in identification of the bacterium. Under harsh environmental conditions, such as loss of a nutritional requirement, these bacteria can convert from a vegetative state to a dormant state, or spore. tetani or botulinum) (soil bacteria), are spore formers. Some gram-positive, but never gram-negative, bacteria, such as members of the genera Bacillus (e.g., B. Murray PhD, F(AAM), F(IDSA), in Medical Microbiology, 2021 Spores