Editing Endospore (section)

{{Short description|Protective structure formed by bacteria}}
{{Distinguish|Endospory in plants}}
[[File:Bacillus subtilis Spore.jpg|thumb|An [[Endospore staining|endospore stain]] of the cell ''[[Bacillus subtilis]]'' showing endospores as green and the vegetative cell as red]]
[[File:Paenibacillus alvei endospore microscope image.tif|thumb|Phase-bright endospores of ''[[Paenibacillus alvei]]'' imaged with phase-contrast microscopy]]
An '''endospore''' is a [[dormancy|dormant]], tough, and non-reproductive structure produced by some [[bacteria]] in the phylum [[Bacillota]].<ref>{{cite book|author1=Murray, Patrick R.|author2=Ellen Jo Baron|title=Manual of Clinical Microbiology|volume=1|location=Washington, D.C.|publisher=ASM|year=2003}}</ref><ref>{{cite encyclopedia|author=C. Michael Hogan |year=2010 |url=http://www.eoearth.org/article/Bacteria?topic=49480 |title=Bacteria |encyclopedia=Encyclopedia of Earth |editor1=Sidney Draggan |editor2=C.J. Cleveland |publisher=National Council for Science and the Environment |location=Washington DC |url-status=dead |archive-url=https://web.archive.org/web/20110511132823/http://www.eoearth.org/article/Bacteria?topic=49480 |archive-date=2011-05-11 }}</ref> The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true [[spore]] (i.e., not an offspring). It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in [[Gram-positive bacteria]]. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other.<ref name=Cornell/> Endospores enable [[bacteria]] to lie dormant for extended periods, even centuries. There are many reports of spores remaining viable over 10,000 years, and revival of spores millions of years old has been claimed. There is one report of viable spores of ''[[Virgibacillus marismortui|Bacillus marismortui]]'' in salt crystals approximately 25 million years old.<ref>{{cite journal | last1 = Cano | first1 = RJ | last2 = Borucki | first2 = MK | year = 1995 | title = Revival and identification of bacterial spores in 25- to 40-million-year-old Dominican amber | journal = Science | volume = 268 | issue = 5213| pages = 1060–1064 | doi = 10.1126/science.7538699 | pmid=7538699| bibcode = 1995Sci...268.1060C }}</ref><ref name="Ringo2004">{{cite book|last1=Ringo|first1=John|title=Fundamental Genetics|chapter=Reproduction of Bacteria|year=2004|pages=153–160|doi=10.1017/CBO9780511807022.018|isbn=9780511807022}}</ref> When the [[Environment (biology)|environment]] becomes more favorable, the endospore can reactivate itself into a vegetative state. Most types of bacteria cannot change to the endospore form. Examples of bacterial [[species]] that can form endospores include ''[[Bacillus cereus]]'', ''[[Bacillus anthracis]]'', ''[[Bacillus thuringiensis]]'', ''[[Clostridium botulinum]]'', and ''[[Clostridium tetani]]''.<ref>{{DorlandsDict|three/000035434|endospore}}</ref> Endospore formation is not found among ''[[Archaea]]''.<ref name="Brock">{{cite book|last1=Madigan|first1=Michael T.|last2=Bender|first2=Kelly S.|last3=Buckley|first3=Daniel H.|last4=Sattley|first4=W. Matthew|last5=Stahl|first5=David A.|title=Brock Biology of Microorganisms|chapter=Microbial Cell Structure and Function|year=2018|pages=92|publisher=Pearson |isbn=9781292235103}}</ref>

The endospore consists of the bacterium's [[DNA]], [[ribosomes]] and large amounts of [[dipicolinic acid]]. Dipicolinic acid is a spore-specific chemical that appears to help in the ability for endospores to maintain dormancy. This chemical accounts for up to 10% of the spore's dry weight.<ref name=Cornell/>

Endospores can survive without nutrients. They are resistant to [[ultraviolet radiation]], [[desiccation]], high temperature, extreme freezing and chemical [[disinfectants]]. Thermo-resistant endospores were first hypothesized by [[Ferdinand Cohn]] after studying ''Bacillus subtilis'' growth on cheese after boiling the cheese. 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."<ref name="BBC-2011">{{cite web |author=BBC Staff |title=Impacts 'more likely' to have spread life from Earth |url=https://www.bbc.co.uk/news/science-environment-14637109 |date=23 August 2011 |publisher=[[BBC]] |access-date=2011-08-24 |archive-url=https://web.archive.org/web/20110824155136/http://www.bbc.co.uk/news/science-environment-14637109 |archive-date=24 August 2011 |url-status=live }}</ref>  Common antibacterial agents that work by destroying vegetative cell walls do not affect endospores. Endospores are commonly found in soil and water, where they may survive for long periods of time. A variety of different microorganisms form "spores" or "cysts", but the endospores of [[Bacillota|low G+C gram-positive bacteria]] are by far the most resistant to harsh conditions.<ref name=Cornell/>

Some classes of bacteria can turn into exospores, also known as [[microbial cyst]]s, instead of endospores. Exospores and endospores are two kinds of "hibernating" or dormant stages seen in some classes of microorganisms.
 [[File:Endospore Formation.png|thumb|Formation of an endospore through the process of sporulation.]]