How does the formation of an endospore aid the bacteria

Microorganisms sense and adapt to changes in their environment. When favored nutrients are exhausted, some bacteria may become motile to seek out nutrients, or they may produce enzymes to exploit alternative resources. This complex developmental process is often initiated in response to nutrient deprivation. It allows the bacterium to produce a dormant and highly resistant cell to preserve the cell's genetic material in times of extreme stress.

Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include high temperature, high UV irradiation, desiccation, chemical damage and enzymatic destruction.

The extraordinary resistance properties of endospores make them of particular importance because they are not readily killed by many antimicrobial treatments. The resilience of an endospore can be explained in part by its unique cellular structure.

The outer proteinaceous coat surrounding the spore provides much of the chemical and enzymatic resistance. Beneath the coat resides a very thick layer of specialized peptidoglycan called the cortex. Proper cortex formation is needed for dehydration of the spore core, which aids in resistance to high temperature.

A germ cell wall resides under the cortex. This layer of peptidoglycan will become the cell wall of the bacterium after the endospore germinates. The inner membrane, under the germ cell wall, is a major permeability barrier against several potentially damaging chemicals.

The center of the endospore, the core, exists in a very dehydrated state and houses the cell's DNA, ribosomes and large amounts of dipicolinic acid. An endospore is a dormant , tough, and non-reproductive structure produced by a small number of bacteria from the Firmicute phylum. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme , temperature, starvation, and chemical disinfectants.

Endospores are commonly found in soil and water, where they may survive for long periods of time. Some bacteria produce exospores or cysts instead. In contrast to eukaryotic spores , which are produced by many eukaryotes for reproductive purposes, bacteria will produce a single endospore internally.

The spore is often surrounded by a thin covering known as the exosporium , which overlies the spore coat. The spore coat is impermeable to many toxic molecules and may also contain enzymes that are involved in germination. The cortex lies beneath the spore coat and consists of peptidoglycan. The core wall lies beneath the cortex and surrounds the protoplast or core of the endospore. The core has normal cell structures, such as DNA and ribosomes , but is metabolically inactive.

Dipicolinic acid could be responsible for the heat resistance of the spore, and calcium may aid in resistance to heat and oxidizing agents. However, mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work [1]. 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. Examples of bacteria having terminal endospores include Clostridium tetani , the pathogen which causes the disease tetanus.

Bacteria having a centrally placed endospore include Bacillus cereus , and those having a subterminal endospore include Bacillus subtilis. Sometimes the endospore can be so large the cell can be distended around the endospore, this is typical of Clostridium tetani. Visualising endospores under the light microscope can be difficult due to the impermeability of the endospore wall to dyes and stains. While the rest of a bacterial cell may stain, the endospore is left colourless.

To combat this, a special stain technique called a Moeller stain is used. Bacteria having a centrally placed endospore include Bacillus cereus, and those having a subterminal endospore include Bacillus subtilis. Sometimes the endospore can be so large that the cell can be distended around the endospore.

This is typical of Clostridium tetani. When a bacterium detects environmental conditions are becoming unfavorable it may start the process of endosporulation, which takes about eight hours. The DNA is replicated and a membrane wall known as a spore septum begins to form between it and the rest of the cell.

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. Calcium dipicolinate is incorporated into the forespore during this time. Next the peptidoglycan cortex forms between the two layers and the bacterium adds a spore coat to the outside of the forespore.

Sporulation is now complete, and the mature endospore will be released when the surrounding vegetative cell is degraded. While resistant to extreme heat and radiation, endospores can be destroyed by burning or by autoclaving.

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. This indirect method is called Tyndallization. It was the usual method for a while in the late 19 th century before the advent of inexpensive autoclaves. Prolonged exposure to ionising radiation, such as x-rays and gamma rays, will also kill most endospores.

Reactivation of the endospore occurs when conditions are more favourable and involves activation, germination, and outgrowth. Even if an endospore is located in plentiful nutrients, it may fail to germinate unless activation has taken place.