Endospore
His notion of spores being the reproductive mechanism for the growth was a large blow to the previous suggestions of spontaneous generation.
Astrophysicist Steinn Sigurdsson said "There are viable bacterial spores that have been found that are 40 million years old on Earth—and we know they're very hardened to radiation.
"[8] Common antibacterial agents that work by destroying vegetative cell walls do not affect endospores.
A variety of different microorganisms form "spores" or "cysts", but the endospores of low G+C gram-positive bacteria are by far the most resistant to harsh conditions.
[10] The X-ray diffraction pattern of purified B. subtilis endospores indicates the presence of a component with a regular periodic structure, which Kadota and Iijima speculated might be formed from a keratin-like protein.
These proteins tightly bind and condense the DNA, and are in part responsible for resistance to UV light and DNA-damaging chemicals.
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.
Examples of bacteria having terminal endospores include Clostridium tetani, the pathogen that causes the disease tetanus.
Under conditions of starvation, especially the lack of carbon and nitrogen sources, a single endospore forms within some of the bacteria through a process called sporulation.
The inner membrane that surrounds this core leads to the endospore's resistance against UV light and harsh chemicals that would normally destroy microbes.
Unlike persister cells, endospores are the result of a morphological differentiation process triggered by nutrient limitation (starvation) in the environment; endosporulation is initiated by quorum sensing within the "starving" population.
[16]: 141 Most disinfectants such as household cleaning products, alcohols, quaternary ammonium compounds and detergents have little effect on endospores.
While significantly resistant to heat and radiation, endospores can be destroyed by burning or by autoclaving at a temperature exceeding the boiling point of water, 100 °C.
They will germinate within a day or two with the right environmental conditions, and then the vegetative cells, not as hardy as endospores, can be straightforwardly destroyed.
The endospores of certain types of (typically non-pathogenic) bacteria, such as Geobacillus stearothermophilus, are used as probes to verify that an autoclaved item has been rendered truly sterile: a small capsule containing the spores is put into the autoclave with the items; after the cycle the content of the capsule is cultured to check if anything will grow from it.
[18] In hospitals, endospores on delicate invasive instruments such as endoscopes are killed by low-temperature, and non-corrosive, ethylene oxide sterilizers.
[19] In contrast, "high level disinfection" does not kill endospores but is used for instruments such as a colonoscope that do not enter sterile bodily cavities.
It is commonly characterised by rupture or absorption of the spore coat, swelling of the endospore, an increase in metabolic activity, and loss of resistance to environmental stress.
It is believed that the macromolecule accountable for maintaining the dormant state has a protein coat rich in cystine, stabilized by S-S linkages.
This conformational change in the protein is thought to be responsible for exposing active enzymatic sites necessary for endospore germination.
In 1995, Raul Cano of California Polytechnic State University found bacterial spores in the gut of a fossilized bee trapped in amber from a tree in the Dominican Republic.
The spores germinated when the amber was cracked open and the material from the gut of the bee was extracted and placed in nutrient medium.
After the spores were analyzed by microscopy, it was determined that the cells were very similar to Lysinibacillus sphaericus which is found in bees in the Dominican Republic today.
[16] According to WHO veterinary documents, B. anthracis sporulates when it sees oxygen instead of the carbon dioxide present in mammal blood; this signals to the bacteria that it has reached the end of the animal, and an inactive dispersable morphology is useful.
Once outside the host, sporulation commences upon exposure to the air and the spore forms are essentially the exclusive phase in the environment.
