Editing Cyanobacteria (section)

==== 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>