Editing Endospore (section)

==Formation and destruction==
[[File:Sporulation.png|thumb|Endospore formation and cycle]]
{{Further|Bacterial morphological plasticity}}
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.<ref>{{Cite web|url=https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Kaiser)/Unit_1%3A_Introduction_to_Microbiology_and_Prokaryotic_Cell_Anatomy/2%3A_The_Prokaryotic_Cell_-_Bacteria/2.4%3A_Cellular_Components_within_the_Cytoplasm/2.4E%3A_Endospores|title=2.4E: Endospores|date=2016-03-02|website=Biology LibreTexts|language=en|access-date=2019-12-30}}</ref>

When a bacterium detects environmental conditions are becoming unfavourable 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, the calcium salt of dipicolinic acid, is incorporated into the forespore during this time. The dipicolinic acid helps stabilize the proteins and DNA in the endospore.<ref name=Pommerville>{{cite book|last=Pommerville|first=Jeffrey C.|title=Fundamentals of microbiology|year=2014|publisher=Jones & Bartlett Learning|location=Burlington, MA|isbn=978-1449688615|edition=10th}}</ref>{{rp|141}} Next the peptidoglycan cortex forms between the two layers and the bacterium adds a spore coat to the outside of the forespore. In the final stages of endospore formation the newly forming endospore is dehydrated and allowed to mature before being released from the mother cell.<ref name=Cornell/> The cortex is what makes the endospore so resistant to temperature. The cortex contains an inner membrane known as the core. The inner membrane that surrounds this core leads to the endospore's resistance against [[Ultraviolet|UV light]] and harsh chemicals that would normally destroy microbes.<ref name=Cornell/> Sporulation is now complete, and the mature endospore will be released when the surrounding vegetative cell is degraded.

Endospores are resistant to most agents that would normally kill the vegetative cells they formed from. Unlike [[persister cell]]s, 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.<ref name=Pommerville/>{{rp|141}}Most disinfectants such as household cleaning products, [[alcohols]], [[quaternary ammonium compounds]] and [[detergents]] have little effect on endospores. However, sterilant [[alkylation|alkylating]] agents such as [[ethylene oxide]] (ETO), and 10% bleach are effective against endospores. To kill most [[anthrax]] spores, standard [[household bleach]] (with 10% [[sodium hypochlorite]]) must be in contact with the spores for at least several minutes; a very small proportion of spores can survive longer than 10 minutes in such a solution.<ref>{{cite journal|last=Heninger|first=Sara|author2=Christine A. Anderson |author3=Gerald Beltz |author4=Andrew B. Onderdonk |title=Decontamination of Bacillus anthracis Spores: Evaluation of Various Disinfectants|journal= Applied Biosafety|date=January 1, 2009|volume=14|issue=1|pages=7–10|pmid=20967138|pmc=2957119|doi=10.1177/153567600901400103}}</ref> Higher concentrations of bleach are not more effective, and can cause some types of bacteria to aggregate and thus survive.

While significantly resistant to heat and radiation, endospores can be destroyed by burning or by [[autoclave|autoclaving]] at a temperature exceeding the boiling point of water, 100&nbsp;°C. Endospores are able to survive at 100&nbsp;°C for hours, although the larger the number of hours the fewer that will survive. 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, not as hardy as endospores, can be straightforwardly destroyed. This indirect method is called [[Tyndallization]]. It was the usual method for a while in the late 19th century before the introduction of inexpensive autoclaves. Prolonged exposure to [[ionising radiation]], such as [[x-ray]]s and [[gamma ray]]s, will also kill most endospores.

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.  If nothing will grow, then the spores were destroyed and the sterilization was successful.<ref>{{cite web|url=http://www.eplantscience.com/index/microbiology_methods/destructions_microorganisms/the_autoclave.php|title=The Autoclave|access-date=June 18, 2016|archive-url=https://web.archive.org/web/20160303212536/http://www.eplantscience.com/index/microbiology_methods/destructions_microorganisms/the_autoclave.php|archive-date=March 3, 2016|url-status=dead}}</ref>

In hospitals, endospores on delicate invasive instruments such as [[endoscope]]s are killed by low-temperature, and non-corrosive, ethylene oxide sterilizers.  Ethylene oxide is the only low-temperature sterilant to stop outbreaks on these instruments.<ref name="CDC">{{cite web |title=Ethylene Oxide Sterilization {{!}} Disinfection & Sterilization Guidelines {{!}} Guidelines Library {{!}} Infection Control {{!}}CDC |url=https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/ethylene-oxide.html |website=www.cdc.gov |access-date=11 October 2019 |language=en-us |date=4 April 2019 |archive-url=https://web.archive.org/web/20191117130336/https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/ethylene-oxide.html |archive-date=17 November 2019 |url-status=live }}</ref> 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. This latter method uses only warm water, enzymes, and detergents.

Bacterial endospores are resistant to [[Antibiotic|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:
* Calcium dipicolinate, abundant within the endospore, may stabilize and protect the endospore's DNA.
* Small acid-soluble proteins (SASPs) saturate the endospore's DNA and protect it from heat, drying, chemicals, and radiation. They also function as a carbon and energy source for the development of a vegetative bacterium during germination.
* The cortex may osmotically remove water from the interior of the endospore and the dehydration that results is thought to be very important in the endospore's resistance to heat and radiation.
* Finally, DNA repair enzymes contained within the endospore are able to repair damaged DNA during germination.