Editing Cyanobacteria (section)

== Photosynthesis ==
[[File:Cyanobacterium-inline.svg|thumb|upright=1.5| {{center|'''Diagram of a typical cyanobacterial cell'''}}]]
[[File:Cyanobacterial thylakoid membrane.png|thumb|upright=1.5| {{center|'''Cyanobacterial thylakoid membrane'''{{hsp}}<ref>{{cite journal | vauthors = Huokko T, Ni T, Dykes GF, Simpson DM, Brownridge P, Conradi FD, Beynon RJ, Nixon PJ, Mullineaux CW, Zhang P, Liu LN | display-authors = 6 | title = Probing the biogenesis pathway and dynamics of thylakoid membranes | journal = Nature Communications | volume = 12 | issue = 1 | pages = 3475 | date = June 2021 | pmid = 34108457 | pmc = 8190092 | doi = 10.1038/s41467-021-23680-1 | bibcode = 2021NatCo..12.3475H }}</ref>}} Outer and plasma membranes are in blue, thylakoid membranes in gold, glycogen granules in cyan, [[carboxysome]]s (C) in green, and a large dense polyphosphate granule (G) in pink]]

=== Carbon fixation ===
The [[thylakoids]] of cyanobacteria use the energy of [[sunlight]] to drive [[photosynthesis]], a process where the energy of light is used to synthesize [[organic compound]]s from carbon dioxide. Because they are aquatic organisms, they typically employ several strategies which are collectively known as a "{{CO2}} concentrating mechanism" to aid in the acquisition of inorganic carbon ({{CO2}} or [[bicarbonate]]). Among the more specific strategies is the widespread prevalence of the bacterial microcompartments known as [[carboxysome]]s,<ref name="KerfeldHeinhorst2010">{{cite journal | vauthors = Kerfeld CA, Heinhorst S, Cannon GC | title = Bacterial microcompartments | journal = Annual Review of Microbiology | volume = 64 | issue = 1 | pages = 391–408 | year = 2010 | pmid = 20825353 | pmc = 6022854 | doi = 10.1146/annurev.micro.112408.134211 }}</ref> which co-operate with active transporters of CO<sub>2</sub> and bicarbonate, in order to accumulate bicarbonate into the cytoplasm of the cell.<ref>{{cite journal | vauthors = Rae BD, Long BM, Badger MR, Price GD | title = Functions, compositions, and evolution of the two types of carboxysomes: polyhedral microcompartments that facilitate CO2 fixation in cyanobacteria and some proteobacteria | journal = Microbiology and Molecular Biology Reviews | volume = 77 | issue = 3 | pages = 357–379 | date = September 2013 | pmid = 24006469 | pmc = 3811607 | doi = 10.1128/MMBR.00061-12 }}</ref> Carboxysomes are [[Icosahedron|icosahedral]] structures composed of hexameric shell proteins that assemble into cage-like structures that can be several hundreds of nanometres in diameter. It is believed that these structures tether the {{CO2}}-fixing enzyme, [[RuBisCO]], to the interior of the shell, as well as the enzyme [[carbonic anhydrase]], using [[metabolic channeling]] to enhance the local {{CO2}} concentrations and thus increase the efficiency of the RuBisCO enzyme.<ref name="LongBadger2007">{{cite journal | vauthors = Long BM, Badger MR, Whitney SM, Price GD | title = Analysis of carboxysomes from Synechococcus PCC7942 reveals multiple Rubisco complexes with carboxysomal proteins CcmM and CcaA | journal = The Journal of Biological Chemistry | volume = 282 | issue = 40 | pages = 29323–29335 | date = October 2007 | pmid = 17675289 | doi = 10.1074/jbc.M703896200 | doi-access = free }}</ref>

=== Electron transport ===
In contrast to [[purple bacteria]] and other bacteria performing [[anoxygenic photosynthesis]], thylakoid membranes of cyanobacteria are not continuous with the plasma membrane but are separate compartments.<ref name="Vothknecht&Westhoff20012">{{cite journal | vauthors = Vothknecht UC, Westhoff P | title = Biogenesis and origin of thylakoid membranes | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1541 | issue = 1–2 | pages = 91–101 | date = December 2001 | pmid = 11750665 | doi = 10.1016/S0167-4889(01)00153-7 | doi-access = free }}</ref> The photosynthetic machinery is embedded in the [[thylakoid]] membranes, with [[phycobilisome]]s acting as [[Light-harvesting complex|light-harvesting antennae]] attached to the membrane, giving the green pigmentation observed (with wavelengths from 450&nbsp;nm to 660&nbsp;nm) in most cyanobacteria.<ref name="Sobiechowska-Sasim_2014">{{cite journal | vauthors = Sobiechowska-Sasim M, Stoń-Egiert J, Kosakowska A | title = Quantitative analysis of extracted phycobilin pigments in cyanobacteria-an assessment of spectrophotometric and spectrofluorometric methods | journal = Journal of Applied Phycology | volume = 26 | issue = 5 | pages = 2065–2074 | date = February 2014 | pmid = 25346572 | pmc = 4200375 | doi = 10.1007/s10811-014-0244-3 | bibcode = 2014JAPco..26.2065S }}</ref>

While most of the high-energy [[electron]]s derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons may be donated to the external environment via [[electrogenic]] activity.<ref name="Pisciotta JM, Zou Y, Baskakov IV 2010 e108212">{{cite journal | vauthors = Pisciotta JM, Zou Y, Baskakov IV | title = Light-dependent electrogenic activity of cyanobacteria | journal = PLOS ONE | volume = 5 | issue = 5 | pages = e10821 | date = May 2010 | pmid = 20520829 | pmc = 2876029 | doi = 10.1371/journal.pone.0010821 | veditors = Yang CH | doi-access = free | bibcode = 2010PLoSO...510821P }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}
</ref>

==== Respiration ====
[[Cellular respiration|Respiration]] in cyanobacteria can occur in the thylakoid membrane alongside photosynthesis,<ref name="Vermaas_2001">{{cite book |title=Photosynthesis and Respiration in Cyanobacteria. eLS. | vauthors = Vermaas WF |date=2001 |publisher=[[John Wiley & Sons]], Ltd |isbn=978-0-470-01590-2 |doi=10.1038/npg.els.0001670 |chapter=Photosynthesis and Respiration in Cyanobacteria}}</ref> with their photosynthetic [[Electron transport chain|electron transport]] sharing the same compartment as the components of respiratory electron transport. While the goal of photosynthesis is to store energy by building carbohydrates from CO<sub>2</sub>, respiration is the reverse of this, with carbohydrates turned back into CO<sub>2</sub> accompanying energy release.

Cyanobacteria appear to separate these two processes with their plasma membrane containing only components of the respiratory chain, while the thylakoid membrane hosts an interlinked respiratory and photosynthetic electron transport chain.<ref name="Vermaas_2001" /> Cyanobacteria use electrons from [[succinate dehydrogenase]] rather than from [[Nicotinamide adenine dinucleotide phosphate|NADPH]] for respiration.<ref name="Vermaas_2001" />

Cyanobacteria only respire during the night (or in the dark) because the facilities used for electron transport are used in reverse for photosynthesis while in the light.<ref name="Armstrong_2014">{{cite book |url=https://www.press.uchicago.edu/ucp/books/book/chicago/H/bo16465693.html |title=How the Earth Turned Green: A Brief 3.8-Billion-Year History of Plants | vauthors = Armstronf JE |date=2015 |publisher=The [[University of Chicago Press]] |isbn=978-0-226-06977-7}}</ref>

==== Electron transport chain ====
Many cyanobacteria are able to reduce nitrogen and carbon dioxide under [[Aerobic cellular respiration|aerobic]] conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of [[photosystem]] (PS) II and I ([[Z-scheme]]). In contrast to [[green sulfur bacteria]] which only use one photosystem, the use of water as an electron donor is energetically demanding, requiring two photosystems.<ref name="Klatt_2016">{{cite journal | vauthors = Klatt JM, de Beer D, Häusler S, Polerecky L | title = Cyanobacteria in Sulfidic Spring Microbial Mats Can Perform Oxygenic and Anoxygenic Photosynthesis Simultaneously during an Entire Diurnal Period | journal = Frontiers in Microbiology | volume = 7 | pages = 1973 | date = 2016 | pmid = 28018309 | pmc = 5156726 | doi = 10.3389/fmicb.2016.01973 | doi-access = free }}</ref>

Attached to the thylakoid membrane, [[phycobilisome]]s act as [[Light-harvesting complex|light-harvesting antennae]] for the photosystems.<ref>{{cite journal | vauthors = Grossman AR, Schaefer MR, Chiang GG, Collier JL | title = The phycobilisome, a light-harvesting complex responsive to environmental conditions | journal = Microbiological Reviews | volume = 57 | issue = 3 | pages = 725–749 | date = September 1993 | pmid = 8246846 | pmc = 372933 | doi = 10.1128/MMBR.57.3.725-749.1993 }}</ref> The phycobilisome components ([[phycobiliprotein]]s) are responsible for the blue-green pigmentation of most cyanobacteria.<ref>{{Cite web |url=http://www.webexhibits.org/causesofcolor/5D.html |title=Colors from bacteria {{!}} Causes of Color |website=www.webexhibits.org |access-date=2018-01-22}}</ref> The variations on this theme are due mainly to [[carotenoid]]s and [[phycoerythrin]]s that give the cells their red-brownish coloration. In some cyanobacteria, the color of light influences the composition of the phycobilisomes.<ref>{{cite book |doi=10.1016/B978-012373944-5.00250-9 | vauthors = Garcia-Pichel F |chapter=Cyanobacteria |title=Encyclopedia of Microbiology |edition=third |pages=107–24 | veditors = Schaechter M |isbn=978-0-12-373944-5 |year=2009| publisher = Elsevier }}</ref><ref>{{cite journal | vauthors = Kehoe DM | title = Chromatic adaptation and the evolution of light color sensing in cyanobacteria | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 20 | pages = 9029–9030 | date = May 2010 | pmid = 20457899 | pmc = 2889117 | doi = 10.1073/pnas.1004510107 | doi-access = free | bibcode = 2010PNAS..107.9029K }}</ref> In green light, the cells accumulate more phycoerythrin, which absorbs green light, whereas in red light they produce more [[phycocyanin]] which absorbs red. Thus, these bacteria can change from brick-red to bright blue-green depending on whether they are exposed to green light or to red light.<ref>{{cite journal | vauthors = Kehoe DM, Gutu A | title = Responding to color: the regulation of complementary chromatic adaptation | journal = Annual Review of Plant Biology | volume = 57 | pages = 127–150 | date = 2006 | issue = 1 | pmid = 16669758 | doi = 10.1146/annurev.arplant.57.032905.105215 | bibcode = 2006AnRPB..57..127K }}</ref> This process of "complementary chromatic adaptation" is a way for the cells to maximize the use of available light for photosynthesis.

A few genera lack phycobilisomes and have [[chlorophyll b]] instead (''[[Prochloron]]'', ''[[Prochlorococcus]]'', ''Prochlorothrix''). These were originally grouped together as the [[Prochlorophyta|prochlorophytes]] or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria. For this reason, they are now considered as part of the cyanobacterial group.<ref>{{cite journal | vauthors = Palenik B, Haselkorn R | title = Multiple evolutionary origins of prochlorophytes, the chlorophyll b-containing prokaryotes | journal = Nature | volume = 355 | issue = 6357 | pages = 265–267 | date = January 1992 | pmid = 1731224 | doi = 10.1038/355265a0 | bibcode = 1992Natur.355..265P }}</ref><ref>{{cite journal | vauthors = Urbach E, Robertson DL, Chisholm SW | title = Multiple evolutionary origins of prochlorophytes within the cyanobacterial radiation | journal = Nature | volume = 355 | issue = 6357 | pages = 267–270 | date = January 1992 | pmid = 1731225 | doi = 10.1038/355267a0 | bibcode = 1992Natur.355..267U }}</ref>

==== Metabolism ====
In general, photosynthesis in cyanobacteria uses water as an [[Redox|electron donor]] and produces [[oxygen]] as a byproduct, though some may also use [[hydrogen sulfide]]<ref name="Cohen Y, Jørgensen BB, Revsbech NP, Poplawski R 19862">{{cite journal | vauthors = Cohen Y, Jørgensen BB, Revsbech NP, Poplawski R | title = Adaptation to Hydrogen Sulfide of Oxygenic and Anoxygenic Photosynthesis among Cyanobacteria | journal = Applied and Environmental Microbiology | volume = 51 | issue = 2 | pages = 398–407 | date = February 1986 | pmid = 16346996 | pmc = 238881 | doi = 10.1128/AEM.51.2.398-407.1986 | bibcode = 1986ApEnM..51..398C }}</ref> a process which occurs among other photosynthetic bacteria such as the [[purple sulfur bacteria]].

[[Carbon dioxide]] is reduced to form [[carbohydrate]]s via the [[Calvin cycle]].<ref>{{cite book |title=Molecular Mechanisms of Photosynthesis | vauthors = Blankenship RE |author1-link=Robert E. Blankenship |publisher=[[Wiley-Blackwell]] |year=2014 |isbn=978-1-4051-8975-0 |pages=147–73}}</ref> The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria.<ref name="Och_2012">{{cite journal | vauthors = Och LM, Shields-Zhou GA |title=The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling |journal=[[Earth-Science Reviews]] |volume=110 |issue=1–4 |pages=26–57 |doi=10.1016/j.earscirev.2011.09.004 |date=January 2012 |bibcode=2012ESRv..110...26O}}</ref> They are often found as [[symbiont]]s with a number of other groups of organisms such as fungi (lichens), [[coral]]s, [[pteridophyte]]s (''[[Azolla]]''), [[angiosperm]]s (''[[Gunnera]]''), etc.<ref>{{cite book | vauthors = Adams DG, Bergman B, Nierzwicki-Bauer SA, Duggan PS, Rai AN, Schüßler A | chapter = Cyanobacterial-Plant Symbioses | veditors = Rosenberg E, DeLong EF, Lory S, Stackebrandt E, Thompson F |title=The Prokaryotes  |date=2013 |publisher=Springer, Berlin, Heidelberg |isbn=978-3-642-30193-3 |pages=359–400 |doi=10.1007/978-3-642-30194-0_17}}</ref> The carbon metabolism of cyanobacteria include the incomplete [[Citric acid cycle|Krebs cycle]],<ref>{{cite journal | vauthors = Zhang S, Bryant DA | title = The tricarboxylic acid cycle in cyanobacteria | journal = Science | volume = 334 | issue = 6062 | pages = 1551–1553 | date = December 2011 | pmid = 22174252 | doi = 10.1126/science.1210858 | bibcode = 2011Sci...334.1551Z }}</ref> the [[pentose phosphate pathway]], and [[glycolysis]].<ref>{{cite journal | vauthors = Xiong W, Lee TC, Rommelfanger S, Gjersing E, Cano M, Maness PC, Ghirardi M, Yu J | display-authors = 6 | title = Phosphoketolase pathway contributes to carbon metabolism in cyanobacteria | journal = Nature Plants | volume = 2 | issue = 1 | pages = 15187 | date = December 2015 | pmid = 27250745 | doi = 10.1038/nplants.2015.187 }}</ref>

There are some groups capable of [[heterotrophic]] growth,<ref name="CarrWhitton1973">{{cite book | vauthors = Smith A |chapter=Synthesis of metabolic intermediates | veditors =  Carr NG, Whitton BA |title=The Biology of Blue-green Algae|chapter-url={{google books |plainurl=y |id=fSRPg-D0Jk0C |page=30}} |year=1973 |publisher=University of California Press |isbn=978-0-520-02344-4 |pages=[https://archive.org/details/biologyofbluegre0000carr/page/30 30–] |url=https://archive.org/details/biologyofbluegre0000carr}}</ref> while others are [[parasitic]], causing diseases in invertebrates or algae (e.g., the [[black band disease]]).<ref>{{cite journal | vauthors = Jangoux M |year=1987 |title=Diseases of Echinodermata. I. Agents microorganisms and protistans |journal=Diseases of Aquatic Organisms |volume=2 |pages=147–62 |doi=10.3354/dao002147 |doi-access=free}}</ref><ref>{{cite book |veditors=Kinne O |year=1980 |title=Diseases of Marine Animals |volume=1 |url=https://www.int-res.com/archive/doma_books/DOMA_Vol_I_(general_aspects,_protozoa_to%20gastropoda).pdf |publisher=John Wiley & Sons |location=Chichester, UK |isbn=978-0-471-99584-5}}</ref><ref>{{cite journal | vauthors = Kristiansen A |doi=10.2216/i0031-8884-4-1-19.1 |title=''Sarcinastrum urosporae'', a Colourless Parasitic Blue-green Alga |journal=Phycologia |year=1964 |volume=4 |issue=1 |pages=19–22 |bibcode=1964Phyco...4...19K }}</ref>
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