Editing Cyanobacteria (section)

== Morphology ==
{{main|Cyanobacterial morphology}}
{{multiple image
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 | header    = Diversity in cyanobacteria morphology
 | image1    = Cyanobacteriaunicellularandcolonial020.jpg
 | caption1  = Unicellular and colonial cyanobacteria.<br /><small>scale bars about 10 μm</small>
 | image2    = Simplefilaments022.jpg
 | caption2  = Simple cyanobacterial filaments ''[[Nostocales]]'', ''[[Oscillatoriales]]'' and ''[[Spirulinales]]''
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[[File:Morphological variation within cyanobacterial genera.jpg|thumb|upright=1.8| {{center|'''Morphological variations'''{{hsp}}<ref>{{cite journal | vauthors = Esteves-Ferreira AA, Cavalcanti JH, Vaz MG, Alvarenga LV, Nunes-Nesi A, Araújo WL | title = Cyanobacterial nitrogenases: phylogenetic diversity, regulation and functional predictions | journal = Genetics and Molecular Biology | volume = 40 | issue = 1 suppl 1 | pages = 261–275 | year = 2017 | pmid = 28323299 | pmc = 5452144 | doi = 10.1590/1678-4685-GMB-2016-0050 }}</ref>}}• Unicellular: (a) ''[[Synechocystis]]'' and (b) ''[[Synechococcus elongatus]]''<br />• Non-[[Heterocyst|heterocytous]]: (c) ''[[Arthrospira|Arthrospira maxima]]'',{{center|(d) ''[[Trichodesmium]]'' and (e) ''Phormidium''}}• False- or non-branching heterocytous: (f) ''[[Nostoc]]''{{center|and (g) ''Brasilonema octagenarum''}}• True-branching heterocytous: (h) ''Stigonema'' {{center|<small>(ak) akinetes (fb) false branching (tb) true branching</small>}}]]

{{multiple image |total_width = 410
|image1=Gloeotrichia in Sytox.jpg |caption1=Ball-shaped colony of [[Gloeotrichia|Gloeotrichia echinulata]] stained with [[SYTOX]]
|image2=CyanobacteriaColl1.jpg |caption2=Colonies of ''[[Nostoc pruniforme]]''
}}
Cyanobacteria are variable in morphology, ranging from [[unicellular]] and [[Filamentous cyanobacteria|filamentous]] to [[Colony (biology)|colonial forms]]. Filamentous forms exhibit functional cell differentiation such as [[heterocyst]]s (for nitrogen fixation), [[akinetes]] (resting stage cells), and [[hormogonia]] (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity.<ref name=Claessen2014>{{cite journal | vauthors = Claessen D, Rozen DE, Kuipers OP, Søgaard-Andersen L, van Wezel GP | title = Bacterial solutions to multicellularity: a tale of biofilms, filaments and fruiting bodies | journal = Nature Reviews. Microbiology | volume = 12 | issue = 2 | pages = 115–124 | date = February 2014 | pmid = 24384602 | doi = 10.1038/nrmicro3178 | hdl-access = free | hdl = 11370/0db66a9c-72ef-4e11-a75d-9d1e5827573d | url = https://pure.rug.nl/ws/files/2328477/2014NatRevMicrobiolClaessen.pdf }}</ref><ref>{{cite journal | vauthors = Nürnberg DJ, Mariscal V, Parker J, Mastroianni G, Flores E, Mullineaux CW | title = Branching and intercellular communication in the Section V cyanobacterium Mastigocladus laminosus, a complex multicellular prokaryote | journal = Molecular Microbiology | volume = 91 | issue = 5 | pages = 935–949 | date = March 2014 | pmid = 24383541 | doi = 10.1111/mmi.12506 | hdl-access = free | hdl = 10261/99110 }}</ref><ref name=Herrero2016>{{cite journal | vauthors = Herrero A, Stavans J, Flores E | title = The multicellular nature of filamentous heterocyst-forming cyanobacteria | journal = FEMS Microbiology Reviews | volume = 40 | issue = 6 | pages = 831–854 | date = November 2016 | pmid = 28204529 | doi = 10.1093/femsre/fuw029 | hdl-access = free | hdl = 10261/140753 }}</ref><ref name=Aguilera2021 />

Many cyanobacteria form motile filaments of cells, called [[hormogonium|hormogonia]], that travel away from the main biomass to bud and form new colonies elsewhere.<ref>{{cite journal | vauthors = Risser DD, Chew WG, Meeks JC | title = Genetic characterization of the hmp locus, a chemotaxis-like gene cluster that regulates hormogonium development and motility in Nostoc punctiforme | journal = Molecular Microbiology | volume = 92 | issue = 2 | pages = 222–233 | date = April 2014 | pmid = 24533832 | doi = 10.1111/mmi.12552 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Khayatan B, Bains DK, Cheng MH, Cho YW, Huynh J, Kim R, Omoruyi OH, Pantoja AP, Park JS, Peng JK, Splitt SD, Tian MY, Risser DD | display-authors = 6 | title = A Putative O-Linked β-''N''-Acetylglucosamine Transferase Is Essential for Hormogonium Development and Motility in the Filamentous Cyanobacterium Nostoc punctiforme | journal = Journal of Bacteriology | volume = 199 | issue = 9 | pages = e00075–17 | date = May 2017 | pmid = 28242721 | pmc = 5388816 | doi = 10.1128/JB.00075-17 }}</ref> The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium.{{cn|date=March 2025}}

Some filamentous species can differentiate into several different [[cell (biology)|cell]] types:
* Vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions
* [[Akinete]]s – climate-resistant spores that may form when environmental conditions become harsh
* Thick-walled [[heterocysts]] – which contain the enzyme [[nitrogenase]] vital for [[nitrogen fixation]]<ref>{{cite journal | vauthors = Meeks JC, Elhai J, Thiel T, Potts M, Larimer F, Lamerdin J, Predki P, Atlas R | display-authors = 6 | title = An overview of the genome of Nostoc punctiforme, a multicellular, symbiotic cyanobacterium | journal = Photosynthesis Research | volume = 70 | issue = 1 | pages = 85–106 | date = 2001 | pmid = 16228364 | doi = 10.1023/A:1013840025518 | bibcode = 2001PhoRe..70...85M }}</ref><ref name="Golden_1998">{{cite journal | vauthors = Golden JW, Yoon HS | title = Heterocyst formation in Anabaena | journal = Current Opinion in Microbiology | volume = 1 | issue = 6 | pages = 623–629 | date = December 1998 | pmid = 10066546 | doi = 10.1016/s1369-5274(98)80106-9 }}</ref><ref name="Fay_1992">{{cite journal | vauthors = Fay P | title = Oxygen relations of nitrogen fixation in cyanobacteria | journal = Microbiological Reviews | volume = 56 | issue = 2 | pages = 340–373 | date = June 1992 | pmid = 1620069 | pmc = 372871 | doi = 10.1128/MMBR.56.2.340-373.1992 }}</ref> in an anaerobic environment due to its sensitivity to oxygen.<ref name="Fay_1992" />

Each individual cell (each single cyanobacterium) typically has a thick, gelatinous [[cell wall]].<ref>{{Cite book | veditors = Singh V, Pande PC, Jain DK | chapter = Cyanobacteria, Actinomycetes, Mycoplasma, and Rickettsias |page=72 |title=Text Book of Botany Diversity of Microbes And Cryptogams |publisher=Rastogi Publications |isbn=978-81-7133-889-4 }}</ref> They lack [[flagellum|flagella]], but hormogonia of some species can move about by [[bacterial gliding|gliding]] along surfaces.<ref>{{Cite news |url=http://www.microbiologynotes.com/differences-between-bacteria-and-cyanobacteria/ |title=Differences between Bacteria and Cyanobacteria |date=2015-10-29 |work=Microbiology Notes |access-date=2018-01-21}}</ref> Many of the multicellular filamentous forms of ''[[Oscillatoria]]'' are capable of a waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming [[gas vesicle]]s, as in [[archaea]].<ref>{{cite journal | vauthors = Walsby AE | title = Gas vesicles | journal = Microbiological Reviews | volume = 58 | issue = 1 | pages = 94–144 | date = March 1994 | pmid = 8177173 | pmc = 372955 | doi = 10.1128/MMBR.58.1.94-144.1994 }}</ref> These vesicles are not [[organelle]]s as such. They are not bounded by [[lipid membranes]], but by a protein sheath.

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