Learning Objectives Highlighted Bacterium Endospores are dormant alternate life forms produced by the genus Bacillus, the genus Clostridium, and a number other genera of bacteria, including Desulfotomaculum, Sporosarcina, Sporolactobacillus, Oscillospira, and Thermoactinomyces. Bacillus species (see Figure \(\PageIndex{1}\)) are obligate aerobes that live in soil while Clostridium species (see Figure \(\PageIndex{2}\)) are obligate anaerobes often found as normal flora of the gastrointestinal tract in animals.
Formation of EndosporesUnder conditions of starvation, especially the lack of carbon and nitrogen sources, a single endospores form within some of the bacteria. The process is called sporulation . First the DNA replicates (Figure \(\PageIndex{3}\), step 1)and a cytoplasmic membrane septum forms at one end of the cell (Figure \(\PageIndex{3}\). step 3). A second layer of cytoplasmic membrane then forms around one of the DNA molecules (Figure \(\PageIndex{3}\), step 4) - the one that will become part of the endospore - to form a forespore (Figure \(\PageIndex{3}\), step 5). Both of these membrane layers then synthesize peptidoglycan in the space between them to form the first protective coat, the cortex (Figure \(\PageIndex{3}\), step 6) that lies adjacent to the germ cell wall that will eventually form the cell wall of the bacterium upon germination. Calcium dipocolinate is also incorporated into the forming endospore. A spore coat composed of a keratin-like protein then forms around the cortex (Figure \(\PageIndex{3}\), step 7). Sometimes an outer membrane composed of lipid and protein and called an exosporium is also seen (Figure \(\PageIndex{3}\), step 8). Finally, the remainder of the bacterium is degraded and the endospore is released (Figure \(\PageIndex{3}\), step 9). Sporulation generally takes around 15 hours. The process is summarized in Figure \(\PageIndex{3}\). YouTube animation of endospore formation by Global Institute of Medical Sciences
Endospore Structure (see Figure \(\PageIndex{3}\), step 10)The completed endospore consists of multiple layers of resistant coats (including a cortex, a spore coat, and sometimes an exosporium) surrounding a nucleoid, some ribosomes, RNA molecules, and enzymes.
(Some bacteria produce spore-like structures distinct from endospores. Exospores are heat resistant spores produced by a budding process in members of the genus Metylosinus and Rhodomicrobium. Cysts are resistant to drying and are formed singly within vegetative cells by Azotobacter, Myxococcus, and Sporocytophaga. Conidia are heat-susceptible asexual reproductive spores produced by various genera of branching bacteria belonging to the group Actinomycetes.) Function of EndosporesAn endospore is not a reproductive structure but rather a resistant, dormant survival form of the organism. Endospores are quite resistant to high temperatures (including boiling), most disinfectants, low energy radiation, drying, etc. The endospore can then survive until a variety of environmental stimuli trigger germination , allowing outgrowth of a single vegetative bacterium as shown in Fig 3, step 11 and step 12 and in Figure \(\PageIndex{4}\). Viable endospores have reportedly been isolated from the GI tract of a bee embedded in amber between 25 and 40 million years ago. Viable endospores of a halophilic (salt-loving) bacterium have also reportedly been isolated from fluid inclusions in salt crystals dating back over 250 million years! Bacterial endospores are resistant to antibiotics, most disinfectants, and physical agents such as radiation, boiling, and drying. The impermeability of the spore coat is thought to be responsible for the endospore's resistance to chemicals. The heat resistance of endospores is due to a variety of factors:
, its oxygen requirements, where it normally lives, and what its exotoxin does, explain the sequence of events that led to the person contracting botulism and dying. Endospores and Infectious DiseaseAlthough harmless themselves until they germinate, they are involved in the transmission of some diseases to humans. Infections transmitted to humans by endospores include:
Summary
QuestionsStudy the material in this section and then write out the answers to these questions. Do not just click on the answers and write them out. This will not test your understanding of this tutorial.
What is the function of a bacterial endospore quizlet?A bacterial endospore is a structure formed within a bacterium that is resistant & dormant. The endospore's purpose is to protect the bacterium from poor or unfavorable conditions that hinder its survival. Spores are also resistant to heat & chemicals that would otherwise kill other bacteria.
Which of the following describes an endospore quizlet?Which of the following most accurately describes an endospore? It is a dormant bacterial cell produced under harsh conditions.
What is the advantage of an endospore to a bacteria quizlet?why is an endospore called a resting structure? of what advantage is an endospore to a bacterial cell? because it provides a method for one cell to rest, or survive, as opposed to grow and reproduce. the protective endospore wall allows a bacterium to withstand adverse conditions in the environment.
Which of the following bacteria produce endospores quizlet?What produces endospores? The Gram-positive bacteria Bacillus and Clostridium.
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