Editing Cyanobacteria (section)

== Ecology ==
[[File:Environmental impact of aquatic photosynthetic microorganisms.png|thumb|upright=2|Environmental impact of cyanobacteria and other photosynthetic microorganisms in aquatic systems. Different classes of photosynthetic microorganisms are found in aquatic and marine environments where they form the base of healthy food webs and participate in symbioses with other organisms. However, shifting environmental conditions can result in community dysbiosis, where the growth of opportunistic species can lead to harmful blooms and toxin production with negative consequences to human health, livestock and fish stocks. Positive interactions are indicated by arrows; negative interactions are indicated by closed circles on the ecological model.<ref>{{cite journal | vauthors = Mazard S, Penesyan A, Ostrowski M, Paulsen IT, Egan S | title = Tiny Microbes with a Big Impact: The Role of Cyanobacteria and Their Metabolites in Shaping Our Future | journal = Marine Drugs | volume = 14 | issue = 5 | page = 97 | date = May 2016 | pmid = 27196915 | pmc = 4882571 | doi = 10.3390/md14050097 | doi-access = free }}</ref>]]

Cyanobacteria can be found in almost every terrestrial and [[aquatic habitat]]&nbsp;– [[ocean]]s, [[fresh water]], damp soil, temporarily moistened rocks in [[desert]]s, bare rock and soil, and even [[Antarctic]] rocks. They can occur as [[planktonic]] cells or form [[phototrophic biofilms]]. They are found inside stones and shells (in [[endolithic ecosystem]]s).<ref>{{cite journal | vauthors = de los Ríos A, Grube M, Sancho LG, Ascaso C | title = Ultrastructural and genetic characteristics of endolithic cyanobacterial biofilms colonizing Antarctic granite rocks | journal = FEMS Microbiology Ecology | volume = 59 | issue = 2 | pages = 386–395 | date = February 2007 | pmid = 17328119 | doi = 10.1111/j.1574-6941.2006.00256.x | bibcode = 2007FEMME..59..386D | doi-access = free }}</ref> A few are [[endosymbiont]]s in [[lichen]]s, plants, various [[protist]]s, or [[Sea sponge|sponges]] and provide energy for the [[Host (biology)|host]]. Some live in the fur of [[sloth]]s, providing a form of [[camouflage]].<ref>{{cite book | vauthors = Vaughan T |title=Mammalogy |year=2011 |publisher=Jones and Barlett |page=21 |url={{google books|plainurl=y |id=LD1nDlzXYicC |page=21}} |isbn=978-0763762995}}</ref>

Aquatic cyanobacteria are known for their extensive and highly visible [[Algal bloom|blooms]] that can form in both [[freshwater]] and marine environments. The blooms can have the appearance of blue-green paint or scum. These blooms can be [[toxic]], and frequently lead to the closure of recreational waters when spotted. [[Marine bacteriophage]]s are significant [[parasites]] of unicellular marine cyanobacteria.<ref>{{cite magazine | vauthors = Schultz N |date=30 August 2009 |url=https://www.newscientist.com/article/mg20327235.000-photosynthetic-viruses-keep-worlds-oxygen-levels-up.html |title=Photosynthetic viruses keep world's oxygen levels up |magazine=[[New Scientist]]}}</ref>

Cyanobacterial growth is favoured in ponds and lakes where waters are calm and have little turbulent mixing.<ref name="Jöhnk_2008">{{cite journal | vauthors = Jöhnk KD, Huisman J, Sharples J, Sommeijer B, Visser PM, Stroom JM |title=Summer heatwaves promote blooms of harmful cyanobacteria |journal=[[Global Change Biology]] |date=1 March 2008 |volume=14 |issue=3 |pages=495–512 |doi=10.1111/j.1365-2486.2007.01510.x |bibcode=2008GCBio..14..495J |url=https://ir.cwi.nl/pub/12731 }}</ref> Their lifecycles are disrupted when the water naturally or artificially mixes from churning currents caused by the flowing water of streams or the churning water of fountains. For this reason blooms of cyanobacteria seldom occur in rivers unless the water is flowing slowly. Growth is also favoured at higher temperatures which enable ''[[Microcystis]]'' species to outcompete [[diatoms]] and [[green algae]], and potentially allow development of toxins.<ref name="Jöhnk_2008"/>

Based on environmental trends, models and observations suggest cyanobacteria will likely increase their dominance in aquatic environments. This can lead to serious consequences, particularly the contamination of sources of [[drinking water]]. Researchers including [[Linda Lawton]] at [[Robert Gordon University]], have developed techniques to study these.<ref>{{Cite web |title=Linda Lawton – 11th International Conference on Toxic Cyanobacteria |url=http://ictc11.org/speakers/linda-lawton/ |access-date=2021-06-25|language=en-US}}</ref> Cyanobacteria can interfere with [[water treatment]] in various ways, primarily by plugging filters (often large beds of sand and similar media) and by producing [[cyanotoxin]]s, which have the potential to cause serious illness if consumed. Consequences may also lie within fisheries and waste management practices. Anthropogenic [[eutrophication]], rising temperatures, vertical stratification and increased [[atmospheric carbon dioxide]] are contributors to cyanobacteria increasing dominance of aquatic ecosystems.<ref>{{cite journal | vauthors = Paerl HW, Paul VJ | title = Climate change: links to global expansion of harmful cyanobacteria | journal = Water Research | volume = 46 | issue = 5 | pages = 1349–1363 | date = April 2012 | pmid = 21893330 | doi = 10.1016/j.watres.2011.08.002 | bibcode = 2012WatRe..46.1349P }}</ref>

[[File:Cyanobacteriaassociatedwithtufa014 Microcoleus v.jpg|thumb|upright|right|Diagnostic Drawing: Cyanobacteria associated with tufa: ''Microcoleus vaginatus'']]

Cyanobacteria have been found to play an important role in terrestrial habitats and organism communities. It has been widely reported that cyanobacteria [[soil crust]]s help to stabilize soil to prevent [[erosion]] and retain water.<ref>{{cite journal |vauthors=Thomas AD, Dougill AJ |date=15 March 2007 |title=Spatial and temporal distribution of cyanobacterial soil crusts in the Kalahari: Implications for soil surface properties |journal=Geomorphology |volume=85 |issue=1 |pages=17–29 |bibcode=2007Geomo..85...17T |doi=10.1016/j.geomorph.2006.03.029}}</ref> An example of a cyanobacterial species that does so is ''Microcoleus vaginatus''. ''M. vaginatus'' stabilizes soil using a [[polysaccharide]] sheath that binds to sand particles and absorbs water.<ref>{{cite journal |vauthors=Belnap J, Gardner JS |date=1993 |title=Soil Microstructure in Soils of the Colorado Plateau: The Role of the Cyanobacterium Microcoleus Vaginatus |journal=The Great Basin Naturalist |volume=53 |issue=1 |pages=40–47 |jstor=41712756}}</ref> ''M. vaginatus'' also makes a significant contribution to the cohesion of [[biological soil crust]].<ref name="SpatialSelfSegregation">{{cite journal |last1=Nelson |first1=Corey |last2=Giraldo-Silva |first2=Ana |last3=Warsop Thomas |first3=Finlay |last4=Garcia-Pichel |first4=Ferran |date=16 November 2022 |title=Spatial self-segregation of pioneer cyanobacterial species drives microbiome organization in biocrusts |journal=ISME Communications |volume=2 |issue=1 |page=114 |doi=10.1038/s43705-022-00199-0 |pmid=37938289 |pmc=9723579 |bibcode=2022ISMEC...2..114N }}</ref>

Some of these organisms contribute significantly to global ecology and the [[oxygen cycle]]. The tiny marine cyanobacterium ''[[Prochlorococcus]]'' was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean.<ref>{{cite journal | vauthors = Nadis S | title = The cells that rule the seas | journal = Scientific American | volume = 289 | issue = 6 | pages = 52–53 | date = December 2003 | pmid = 14631732 | doi = 10.1038/scientificamerican1203-52 | bibcode = 2003SciAm.289f..52N }}</ref> [[Circadian rhythm]]s were once thought to only exist in eukaryotic cells but many cyanobacteria display a [[bacterial circadian rhythm]].

<blockquote>"Cyanobacteria are arguably the most successful group of [[microorganisms]] on earth. They are the most genetically diverse; they occupy a broad range of habitats across all latitudes, widespread in freshwater, marine, and terrestrial ecosystems, and they are found in the most extreme niches such as hot springs, salt works, and hypersaline bays. [[Photoautotrophic]], oxygen-producing cyanobacteria created the conditions in the planet's early atmosphere that directed the evolution of aerobic metabolism and eukaryotic photosynthesis. Cyanobacteria fulfill vital ecological functions in the world's oceans, being important contributors to global carbon and nitrogen budgets." – Stewart and Falconer<ref name="WalshSmith2011">{{cite book | veditors = Walsh PJ, Smith S, Fleming L, Solo-Gabriele H, Gerwick WH
 |title=Oceans and Human Health: Risks and Remedies from the Seas |chapter-url={{google books |plainurl=y |id=LMZPqW-PmFYC |page=271}} |date=2 September 2011 | vauthors = Stewart I, Falconer IR |chapter=Cyanobacteria and cyanobacterial toxins |pages=271–296 |publisher=[[Academic Press]] |isbn=978-0-08-087782-2}}</ref>
</blockquote>

=== Cyanobionts ===
[[File:Leaf and root colonization by cyanobacteria.jpg|thumb|upright=2|right| {{center|'''Symbiosis with land plants'''{{hsp}}<ref name=Lee2021>{{cite journal | vauthors = Lee SM, Ryu CM | title = Algae as New Kids in the Beneficial Plant Microbiome | journal = Frontiers in Plant Science | volume = 12 | pages = 599742 | date = 4 Feb 2021 | pmid = 33613596 | pmc = 7889962 | doi = 10.3389/fpls.2021.599742 | publisher = Frontiers Media SA | doi-access = free | bibcode = 2021FrPS...1299742L }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref><br />Leaf and root colonization by cyanobacteria}} (1) Cyanobacteria enter the leaf tissue through the [[stomata]] and colonize the intercellular space, forming a cyanobacterial loop.<br /> (2) On the root surface, cyanobacteria exhibit two types of colonization pattern; in the [[root hair]], filaments of ''[[Anabaena]]'' and ''[[Nostoc]]'' species form loose colonies, and in the restricted zone on the root surface, specific ''Nostoc'' species form cyanobacterial colonies.<br /> (3) Co-inoculation with [[2,4-Dichlorophenoxyacetic acid|2,4-D]] and ''Nostoc'' spp. increases para-nodule formation and nitrogen fixation. A large number of ''Nostoc'' spp. isolates colonize the root [[endosphere]] and form para-nodules.<ref name=Lee2021 />]]
{{main|Cyanobiont}}

Some cyanobacteria, the so-called [[cyanobiont]]s (cyanobacterial symbionts), have a [[symbiotic]] relationship with other organisms, both unicellular and multicellular.<ref name=Kim2020 /> As illustrated on the right, there are many examples of cyanobacteria interacting [[symbiotically]] with [[land plant]]s.<ref>{{cite journal |doi=10.1046/j.1469-8137.1999.00352.x |title=Colonization of wheatpara-nodules by the N2-fixing cyanobacterium ''Nostocsp''. Strain 2S9B |year=1999 | vauthors = Gantar M, Elhai J |journal=[[New Phytologist]] |volume=141 |issue=3 |pages=373–379 |doi-access=free}}</ref><ref>{{cite journal |doi=10.1007/s003740000243 |title=Mechanical damage of roots provides enhanced colonization of the wheat endorhizosphere by the dinitrogen-fixing cyanobacterium Nostoc sp. Strain 2S9B |year=2000 | vauthors = Gantar M |journal=Biology and Fertility of Soils |volume=32 |issue=3 |pages=250–255 |bibcode=2000BioFS..32..250G }}</ref><ref name=Treves2016>{{cite journal | vauthors = Treves H, Raanan H, Kedem I, Murik O, Keren N, Zer H, Berkowicz SM, Giordano M, Norici A, Shotland Y, Ohad I, Kaplan A | display-authors = 6 | title = The mechanisms whereby the green alga Chlorella ohadii, isolated from desert soil crust, exhibits unparalleled photodamage resistance | journal = The New Phytologist | volume = 210 | issue = 4 | pages = 1229–1243 | date = June 2016 | pmid = 26853530 | doi = 10.1111/nph.13870 | doi-access = free | bibcode = 2016NewPh.210.1229T }}</ref><ref>{{cite journal | vauthors = Zhu H, Li S, Hu Z, Liu G | title = Molecular characterization of eukaryotic algal communities in the tropical phyllosphere based on real-time sequencing of the 18S rDNA gene | journal = BMC Plant Biology | volume = 18 | issue = 1 | pages = 365 | date = December 2018 | pmid = 30563464 | pmc = 6299628 | doi = 10.1186/s12870-018-1588-7 | doi-access = free | bibcode = 2018BMCPB..18..365Z }}</ref> Cyanobacteria can enter the plant through the [[stomata]] and colonize the intercellular space, forming loops and intracellular coils.<ref>{{cite journal |doi=10.1016/j.revpalbo.2008.06.006 |title=Endophytic cyanobacteria in a 400-million-yr-old land plant: A scenario for the origin of a symbiosis? |year=2009 | vauthors = Krings M, Hass H, Kerp H, Taylor TN, Agerer R, Dotzler N |journal=[[Review of Palaeobotany and Palynology]] |volume=153 |issue=1–2 |pages=62–69|bibcode=2009RPaPa.153...62K }}</ref> ''[[Anabaena]]'' spp. colonize the roots of wheat and cotton plants.<ref>{{cite journal | vauthors = Karthikeyan N, Prasanna R, Sood A, Jaiswal P, Nayak S, Kaushik BD | title = Physiological characterization and electron microscopic investigation of cyanobacteria associated with wheat rhizosphere | journal = Folia Microbiologica | volume = 54 | issue = 1 | pages = 43–51 | year = 2009 | pmid = 19330544 | doi = 10.1007/s12223-009-0007-8 }}</ref><ref name=Babu2015>{{cite journal |doi=10.1007/s10811-014-0322-6 |title=Analysing the colonisation of inoculated cyanobacteria in wheat plants using biochemical and molecular tools |year=2015 | vauthors = Babu S, Prasanna R, Bidyarani N, Singh R |journal=Journal of Applied Phycology |volume=27 |issue=1 |pages=327–338 |bibcode=2015JAPco..27..327B }}</ref><ref name=Bidyarani2015>{{cite journal | vauthors = Bidyarani N, Prasanna R, Chawla G, Babu S, Singh R | title = Deciphering the factors associated with the colonization of rice plants by cyanobacteria | journal = Journal of Basic Microbiology | volume = 55 | issue = 4 | pages = 407–419 | date = April 2015 | pmid = 25515189 | doi = 10.1002/jobm.201400591 }}</ref> ''[[Calothrix]]'' sp. has also been found on the root system of wheat.<ref name=Babu2015 /><ref name=Bidyarani2015 /> [[Monocot]]s, such as wheat and rice, have been colonised by ''[[Nostoc]]'' spp.,<ref name=Gantar1991>{{cite journal |doi=10.1111/j.1469-8137.1991.tb00031.x |title=Colonization of wheat (Triticum vulgare L.) by N2-fixing cyanobacteria: II. An ultrastructural study |year=1991 | vauthors = Gantar M, Kerby NW, Rowell P |journal=[[New Phytologist]] |volume=118 |issue=3 |pages=485–492 |doi-access=free|bibcode=1991NewPh.118..485G }}</ref><ref>{{cite journal |doi=10.1007/s11104-010-0488-x |title=Association of non-heterocystous cyanobacteria with crop plants |year=2010 | vauthors = Ahmed M, Stal LJ, Hasnain S |journal=[[Plant and Soil]] |volume=336 |issue=1–2 |pages=363–375 |bibcode=2010PlSoi.336..363A |url=http://dare.uva.nl/personal/pure/en/publications/association-of-nonheterocystous-cyanobacteria-with-crop-plants(a90f9b12-6bd1-47cc-87c4-389ab649d969).html }}</ref><ref>{{cite journal | vauthors = Hussain A, Hamayun M, Shah ST | title = Root colonization and phytostimulation by phytohormones producing entophytic Nostoc sp. AH-12 | journal = Current Microbiology | volume = 67 | issue = 5 | pages = 624–630 | date = November 2013 | pmid = 23794014 | doi = 10.1007/s00284-013-0408-4 }}</ref><ref>{{cite journal | vauthors = Hussain A, Shah ST, Rahman H, Irshad M, Iqbal A | title = Effect of IAA on in vitro growth and colonization of Nostoc in plant roots | journal = Frontiers in Plant Science | volume = 6 | pages = 46 | year = 2015 | pmid = 25699072 | pmc = 4318279 | doi = 10.3389/fpls.2015.00046 | doi-access = free | bibcode = 2015FrPS....6...46H }}</ref> In 1991, Ganther and others isolated diverse [[heterocystous]] nitrogen-fixing cyanobacteria, including ''Nostoc'', ''Anabaena'' and ''[[Cylindrospermum]]'', from plant root and soil. Assessment of wheat seedling roots revealed two types of association patterns: loose colonization of root hair by ''Anabaena'' and tight colonization of the root surface within a restricted zone by ''Nostoc''.<ref name=Gantar1991 /><ref name=Lee2021 />

[[File:Cyanobacterial symbionts of Ornithocercus dinoflagellate 2.png|thumb|upright=2|left| {{center|'''Cyanobionts of ''Ornithocercus'' dinoflagellates'''{{hsp}}<ref name=Kim2020>{{cite journal | vauthors = Kim M, Choi DH, Park MG | title = Cyanobiont genetic diversity and host specificity of cyanobiont-bearing dinoflagellate Ornithocercus in temperate coastal waters | journal = Scientific Reports | volume = 11 | issue = 1 | pages = 9458 | date = May 2021 | pmid = 33947914 | pmc = 8097063 | doi = 10.1038/s41598-021-89072-z | bibcode = 2021NatSR..11.9458K }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref>}} Live cyanobionts (cyanobacterial symbionts) belonging to ''[[Ornithocercus]]'' [[dinoflagellate]] host consortium<br />(a) ''O. magnificus'' with numerous cyanobionts present in the upper and lower girdle lists (black arrowheads) of the cingulum termed the symbiotic chamber.<br />(b) ''O. steinii'' with numerous cyanobionts inhabiting the symbiotic chamber.<br />(c) Enlargement of the area in (b) showing two cyanobionts that are being divided by binary transverse fission (white arrows).]]

[[File:Cyanobacteria in symbiosis with a diatom.png|thumb|upright=1|right| {{center|[[Epiphytic]] ''[[Calothrix]] ''cyanobacteria (arrows) in symbiosis with a ''[[Chaetoceros]]'' diatom. Scale bar 50 μm.}}]]

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The relationships between [[cyanobiont]]s (cyanobacterial symbionts) and protistan hosts are particularly noteworthy, as some nitrogen-fixing cyanobacteria ([[diazotroph]]s) play an important role in [[Marine primary production|primary production]], especially in nitrogen-limited [[oligotrophic]] oceans.<ref>{{cite journal |doi=10.1126/science.276.5316.1221 |title=Trichodesmium, a Globally Significant Marine Cyanobacterium |year=1997 | vauthors = Capone DG |journal=Science |volume=276 |issue=5316 |pages=1221–1229}}</ref><ref>{{cite journal | vauthors = Falkowski PG, Barber RT, Smetacek V | title = Biogeochemical Controls and Feedbacks on Ocean Primary Production | journal = Science | volume = 281 | issue = 5374 | pages = 200–207 | date = July 1998 | pmid = 9660741 | doi = 10.1126/science.281.5374.200 }}</ref><ref>{{cite journal |doi=10.4319/lo.2007.52.4.1293 |title=CO2 control of Trichodesmium N2 fixation, photosynthesis, growth rates, and elemental ratios: Implications for past, present, and future ocean biogeochemistry |year=2007 | vauthors = Hutchins DA, Fu FX, Zhang Y, Warner ME, Feng Y, Portune K, Bernhardt PW, Mulholland MR |author-link8=Margaret Mulholland |journal=[[Limnology and Oceanography]] |volume=52 |issue=4 |pages=1293–1304 |bibcode=2007LimOc..52.1293H |doi-access=free }}</ref> Cyanobacteria, mostly [[pico-]]sized ''[[Synechococcus]]'' and ''[[Prochlorococcus]]'', are ubiquitously distributed and are the most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems.<ref name="Present and future global distribut"/><ref>{{cite journal | vauthors = Huang S, Wilhelm SW, Harvey HR, Taylor K, Jiao N, Chen F | title = Novel lineages of Prochlorococcus and Synechococcus in the global oceans | journal = The ISME Journal | volume = 6 | issue = 2 | pages = 285–297 | date = February 2012 | pmid = 21955990 | pmc = 3260499 | doi = 10.1038/ismej.2011.106 | bibcode = 2012ISMEJ...6..285H }}</ref><ref name="Partensky-1999"/> In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host.<ref>{{cite book |doi=10.1201/b13853 |title=Stress Biology of Cyanobacteria |date=2013 |publisher=CRC Press |isbn=978-0-429-10135-9 |editor-last1=Srivastava |editor-last2=Rai |editor-last3=Neilan |editor-first1=Ashish Kumar |editor-first2=Amar Nath |editor-first3=Brett A. }}{{pn|date=February 2025}}</ref><ref>{{cite journal | vauthors = Zehr JP, Bench SR, Carter BJ, Hewson I, Niazi F, Shi T, Tripp HJ, Affourtit JP | display-authors = 6 | title = Globally distributed uncultivated oceanic N2-fixing cyanobacteria lack oxygenic photosystem II | journal = Science | volume = 322 | issue = 5904 | pages = 1110–1112 | date = November 2008 | pmid = 19008448 | doi = 10.1126/science.1165340 | bibcode = 2008Sci...322.1110Z }}</ref> However, the physiological functions of most cyanobionts remain unknown. Cyanobionts have been found in numerous protist groups, including [[dinoflagellate]]s, [[tintinnid]]s, [[radiolarian]]s, [[amoebae]], [[diatom]]s, and [[haptophyte]]s.<ref>{{cite book |doi=10.1007/978-4-431-55130-0_19 |chapter=Photosymbiosis in Marine Planktonic Protists |title=Marine Protists |year=2015 | vauthors = Decelle J, Colin S, Foster RA |pages=465–500 |publisher=Springer |location=Tokyo |isbn=978-4-431-55129-4}}</ref><ref>{{cite journal | vauthors = Foster RA, Zehr JP | title = Diversity, Genomics, and Distribution of Phytoplankton-Cyanobacterium Single-Cell Symbiotic Associations | journal = Annual Review of Microbiology | volume = 73 | pages = 435–456 | date = September 2019 | issue = 1 | pmid = 31500535 | doi = 10.1146/annurev-micro-090817-062650 }}</ref> Among these cyanobionts, little is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, particularly in relation to dinoflagellate host.<ref name=Kim2020 />

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=== Collective behaviour ===
{{further|Algal bloom}}

[[File:Collective behaviour and lifestyle choices in single-celled cyanobacteria.webp|thumb|upright=2| {{center|Collective behaviour and  buoyancy strategies in single-celled cyanobacteria{{hsp}}<ref name=Mullineaux2021>{{cite journal | vauthors = Mullineaux CW, Wilde A | title = The social life of cyanobacteria | journal = eLife | volume = 10 | date = June 2021 | pmid = 34132636 | pmc = 8208810 | doi = 10.7554/eLife.70327 | doi-access = free }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref>}}]]

Some cyanobacteria – even single-celled ones – show striking collective behaviours and form colonies (or [[algal bloom|blooms]]) that can float on water and have important ecological roles. For instance, billions of years ago, communities of marine [[Paleoproterozoic]] cyanobacteria could have helped create the [[biosphere]] as we know it by burying carbon compounds and allowing the initial build-up of oxygen in the atmosphere.<ref>{{cite journal | vauthors = Kamennaya NA, Zemla M, Mahoney L, Chen L, Holman E, Holman HY, Auer M, Ajo-Franklin CM, Jansson C | display-authors = 6 | title = High pCO<sub>2</sub>-induced exopolysaccharide-rich ballasted aggregates of planktonic cyanobacteria could explain Paleoproterozoic carbon burial | journal = Nature Communications | volume = 9 | issue = 1 | pages = 2116 | date = May 2018 | pmid = 29844378 | pmc = 5974010 | doi = 10.1038/s41467-018-04588-9 | bibcode = 2018NatCo...9.2116K }}</ref> On the other hand, [[Harmful algal bloom|toxic cyanobacterial bloom]]s are an increasing issue for society, as their toxins can be harmful to animals.<ref name=Huisman2018>{{cite journal | vauthors = Huisman J, Codd GA, Paerl HW, Ibelings BW, Verspagen JM, Visser PM | title = Cyanobacterial blooms | journal = Nature Reviews. Microbiology | volume = 16 | issue = 8 | pages = 471–483 | date = August 2018 | pmid = 29946124 | doi = 10.1038/s41579-018-0040-1 }}</ref> Extreme blooms can also deplete water of oxygen and reduce the penetration of sunlight and visibility, thereby compromising the feeding and mating behaviour of light-reliant species.<ref name=Mullineaux2021 />

As shown in the diagram on the right, bacteria can stay in suspension as individual cells, adhere collectively to surfaces to form biofilms, passively sediment, or flocculate to form suspended aggregates. Cyanobacteria are able to produce sulphated [[polysaccharide]]s (yellow haze surrounding clumps of cells) that enable them to form floating aggregates. In 2021, Maeda et al. discovered that oxygen produced by cyanobacteria becomes trapped in the network of polysaccharides and cells, enabling the microorganisms to form buoyant blooms.<ref name=Maeda2021>{{cite journal | vauthors = Maeda K, Okuda Y, Enomoto G, Watanabe S, Ikeuchi M | title = Biosynthesis of a sulfated exopolysaccharide, synechan, and bloom formation in the model cyanobacterium ''Synechocystis'' sp. strain PCC 6803 | journal = eLife | volume = 10 | date = June 2021 | pmid = 34127188 | pmc = 8205485 | doi = 10.7554/eLife.66538 | doi-access = free }}</ref> It is thought that specific protein fibres known as [[Pilus|pili]] (represented as lines radiating from the cells) may act as an additional way to link cells to each other or onto surfaces. Some cyanobacteria also use sophisticated intracellular [[gas vesicle]]s as floatation aids.<ref name=Mullineaux2021 />

[[File:Model of a clumped cyanobacterial mat.webp|thumb|upright=1.35|left| {{center|Model of a clumped cyanobacterial mat{{hsp}}<ref name=Sim2012>{{cite journal |doi=10.3390/geosciences2040235 |doi-access=free |title=Oxygen-Dependent Morphogenesis of Modern Clumped Photosynthetic Mats and Implications for the Archean Stromatolite Record |year=2012 | vauthors = Sim MS, Liang B, Petroff AP, Evans A, Klepac-Ceraj V, Flannery DT, Walter MR, Bosak T | display-authors = 6 |journal=Geosciences |volume=2 |issue=4 |pages=235–259 |bibcode=2012Geosc...2..235S|hdl=1721.1/85544 |hdl-access=free }} {{Creative Commons text attribution notice|cc=by3|from this source=yes}}</ref>}}]]

[[File:Cyanobacteria guerrero negro.jpg|thumb|upright=1.15| Light microscope view of cyanobacteria from a [[microbial mat]]]]

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The diagram on the left above shows a proposed model of microbial distribution, spatial organization, carbon and O<sub>2</sub> cycling in clumps and adjacent areas. (a) Clumps contain denser cyanobacterial filaments and heterotrophic microbes. The initial differences in density depend on cyanobacterial motility and can be established over short timescales. Darker blue color outside of the clump indicates higher oxygen concentrations in areas adjacent to clumps. Oxic media increase the reversal frequencies of any filaments that begin to leave the clumps, thereby reducing the net migration away from the clump. This enables the persistence of the initial clumps over short timescales; (b) Spatial coupling between photosynthesis and respiration in clumps. Oxygen produced by cyanobacteria diffuses into the overlying medium or is used for aerobic respiration. [[Dissolved inorganic carbon]] (DIC) diffuses into the clump from the overlying medium and is also produced within the clump by respiration. In oxic solutions, high O<sub>2</sub> concentrations reduce the efficiency of CO<sub>2</sub> fixation and result in the excretion of glycolate. Under these conditions, clumping can be beneficial to cyanobacteria if it stimulates the retention of carbon and the assimilation of inorganic carbon by cyanobacteria within clumps. This effect appears to promote the accumulation of [[particulate organic carbon]] (cells, sheaths and heterotrophic organisms) in clumps.<ref name=Sim2012 />

It has been unclear why and how cyanobacteria form communities. Aggregation must divert resources away from the core business of making more cyanobacteria, as it generally involves the production of copious quantities of extracellular material. In addition, cells in the centre of dense aggregates can also suffer from both shading and shortage of nutrients.<ref name=Conradi2019>{{cite journal | vauthors = Conradi FD, Zhou RQ, Oeser S, Schuergers N, Wilde A, Mullineaux CW | title = Factors Controlling Floc Formation and Structure in the Cyanobacterium ''Synechocystis'' sp. Strain PCC 6803 | journal = Journal of Bacteriology | volume = 201 | issue = 19 | date = October 2019 | pmid = 31262837 | pmc = 6755745 | doi = 10.1128/JB.00344-19 }}</ref><ref>{{cite journal | vauthors = Enomoto G, Ikeuchi M | title = Blue-/Green-Light-Responsive Cyanobacteriochromes Are Cell Shade Sensors in Red-Light Replete Niches | journal = iScience | volume = 23 | issue = 3 | pages = 100936 | date = March 2020 | pmid = 32146329 | pmc = 7063230 | doi = 10.1016/j.isci.2020.100936 | bibcode = 2020iSci...23j0936E }}</ref> So, what advantage does this communal life bring for cyanobacteria?<ref name=Mullineaux2021 />

[[File:Cell death in eukaryotes and cyanobacteria.jpg|thumb|upright=2| {{center|'''Cell death in eukaryotes and cyanobacteria'''{{hsp}}<ref name=Aguilera2021>{{cite journal | vauthors = Aguilera A, Klemenčič M, Sueldo DJ, Rzymski P, Giannuzzi L, Martin MV | title = Cell Death in Cyanobacteria: Current Understanding and Recommendations for a Consensus on Its Nomenclature | journal = Frontiers in Microbiology | volume = 12 | pages = 631654 | year = 2021 | pmid = 33746925 | pmc = 7965980 | doi = 10.3389/fmicb.2021.631654 | doi-access = free }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref>}} Types of cell death according to the [[Nomenclature Committee on Cell Death]] (upper panel;<ref>{{cite journal | vauthors = Galluzzi L, Bravo-San Pedro JM, Vitale I, Aaronson SA, Abrams JM, Adam D, Alnemri ES, Altucci L, Andrews D, Annicchiarico-Petruzzelli M, Baehrecke EH, Bazan NG, Bertrand MJ, Bianchi K, Blagosklonny MV, Blomgren K, Borner C, Bredesen DE, Brenner C, Campanella M, Candi E, Cecconi F, Chan FK, Chandel NS, Cheng EH, Chipuk JE, Cidlowski JA, Ciechanover A, Dawson TM, Dawson VL, De Laurenzi V, De Maria R, Debatin KM, Di Daniele N, Dixit VM, Dynlacht BD, El-Deiry WS, Fimia GM, Flavell RA, Fulda S, Garrido C, Gougeon ML, Green DR, Gronemeyer H, Hajnoczky G, Hardwick JM, Hengartner MO, Ichijo H, Joseph B, Jost PJ, Kaufmann T, Kepp O, Klionsky DJ, Knight RA, Kumar S, Lemasters JJ, Levine B, Linkermann A, Lipton SA, Lockshin RA, López-Otín C, Lugli E, Madeo F, Malorni W, Marine JC, Martin SJ, Martinou JC, Medema JP, Meier P, Melino S, Mizushima N, Moll U, Muñoz-Pinedo C, Nuñez G, Oberst A, Panaretakis T, Penninger JM, Peter ME, Piacentini M, Pinton P, Prehn JH, Puthalakath H, Rabinovich GA, Ravichandran KS, Rizzuto R, Rodrigues CM, Rubinsztein DC, Rudel T, Shi Y, Simon HU, Stockwell BR, Szabadkai G, Tait SW, Tang HL, Tavernarakis N, Tsujimoto Y, Vanden Berghe T, Vandenabeele P, Villunger A, Wagner EF, Walczak H, White E, Wood WG, Yuan J, Zakeri Z, Zhivotovsky B, Melino G, Kroemer G | display-authors = 6 | title = Essential versus accessory aspects of cell death: recommendations of the NCCD 2015 | journal = Cell Death and Differentiation | volume = 22 | issue = 1 | pages = 58–73 | date = January 2015 | pmid = 25236395 | pmc = 4262782 | doi = 10.1038/cdd.2014.137 }}</ref> and proposed for cyanobacteria (lower panel). Cells exposed to extreme injury die in an uncontrollable manner, reflecting the loss of structural integrity. This type of cell death is called "accidental cell death" (ACD). "Regulated cell death (RCD)" is encoded by a genetic pathway that can be modulated by genetic or pharmacologic interventions. [[Programmed cell death]] (PCD) is a type of RCD that occurs as a developmental program, and has not been addressed in cyanobacteria yet. RN, regulated necrosis.]]

New insights into how cyanobacteria form blooms have come from a 2021 study on the cyanobacterium ''[[Synechocystis]]''. These use a set of genes that regulate the production and export of sulphated [[polysaccharide]]s, chains of sugar molecules modified with [[sulphate]] groups that can often be found in marine algae and animal tissue. Many bacteria generate extracellular polysaccharides, but sulphated ones have only been seen in cyanobacteria. In ''Synechocystis'' these sulphated polysaccharide help the cyanobacterium form buoyant aggregates by trapping oxygen bubbles in the slimy web of cells and polysaccharides.<ref name=Maeda2021 /><ref name=Mullineaux2021 />

Previous studies on ''Synechocystis'' have shown [[type IV pili]], which decorate the surface of cyanobacteria, also play a role in forming blooms.<ref>{{cite journal | vauthors = Allen R, Rittmann BE, Curtiss R | title = Axenic Biofilm Formation and Aggregation by ''Synechocystis'' sp. Strain PCC 6803 Are Induced by Changes in Nutrient Concentration and Require Cell Surface Structures | journal = Applied and Environmental Microbiology | volume = 85 | issue = 7 | date = April 2019 | pmid = 30709828 | pmc = 6585507 | doi = 10.1128/AEM.02192-18 | bibcode = 2019ApEnM..85E2192A }}</ref><ref name=Conradi2019 /> These retractable and adhesive protein fibres are important for motility, adhesion to substrates and DNA uptake.<ref>{{cite journal | vauthors = Schuergers N, Wilde A | title = Appendages of the cyanobacterial cell | journal = Life | volume = 5 | issue = 1 | pages = 700–715 | date = March 2015 | pmid = 25749611 | pmc = 4390875 | doi = 10.3390/life5010700 | bibcode = 2015Life....5..700S | doi-access = free }}</ref> The formation of blooms may require both type IV pili and Synechan – for example, the pili may help to export the polysaccharide outside the cell. Indeed, the activity of these protein fibres may be connected to the production of extracellular polysaccharides in filamentous cyanobacteria.<ref name=Khayatan2015>{{cite journal | vauthors = Khayatan B, Meeks JC, Risser DD | title = Evidence that a modified type IV pilus-like system powers gliding motility and polysaccharide secretion in filamentous cyanobacteria | journal = Molecular Microbiology | volume = 98 | issue = 6 | pages = 1021–1036 | date = December 2015 | pmid = 26331359 | doi = 10.1111/mmi.13205 | doi-access = free }}</ref> A more obvious answer would be that pili help to build the aggregates by binding the cells with each other or with the extracellular polysaccharide. As with other kinds of bacteria,<ref>{{cite journal | vauthors = Adams DW, Stutzmann S, Stoudmann C, Blokesch M | title = DNA-uptake pili of Vibrio cholerae are required for chitin colonization and capable of kin recognition via sequence-specific self-interaction | journal = Nature Microbiology | volume = 4 | issue = 9 | pages = 1545–1557 | date = September 2019 | pmid = 31182799 | pmc = 6708440 | doi = 10.1038/s41564-019-0479-5 }}</ref> certain components of the pili may allow cyanobacteria from the same species to recognise each other and make initial contacts, which are then stabilised by building a mass of extracellular polysaccharide.<ref name=Mullineaux2021 />

The bubble flotation mechanism identified by Maeda et al. joins a range of known strategies that enable cyanobacteria to control their buoyancy, such as using gas vesicles or accumulating carbohydrate ballasts.<ref>{{cite journal |doi=10.1093/plankt/12.1.161 |title=A computer model of buoyancy and vertical migration in cyanobacteria |year=1990 | vauthors = Kromkamp J, Walsby AE |journal=[[Journal of Plankton Research]] |volume=12 |issue=1 |pages=161–183}}</ref> Type IV pili on their own could also control the position of marine cyanobacteria in the water column by regulating viscous drag.<ref>{{cite journal | vauthors = Aguilo-Ferretjans MD, Bosch R, Puxty RJ, Latva M, Zadjelovic V, Chhun A, Sousoni D, Polin M, Scanlan DJ, Christie-Oleza JA | display-authors = 6 | title = Pili allow dominant marine cyanobacteria to avoid sinking and evade predation | journal = Nature Communications | volume = 12 | issue = 1 | pages = 1857 | date = March 2021 | pmid = 33767153 | pmc = 7994388 | doi = 10.1038/s41467-021-22152-w | bibcode = 2021NatCo..12.1857A }}</ref> Extracellular polysaccharide appears to be a multipurpose asset for cyanobacteria, from floatation device to food storage, defence mechanism and mobility aid.<ref name=Khayatan2015 /><ref name=Mullineaux2021 />

=== Cellular death ===
[[File:Toxins-11-00706-g001.png|thumb|The hypothetical conceptual model coupling programmed cell death (PCD) and the role of microcystins (MCs) in Microcystis. (1) The extracellular stressor (e.g., ultraviolet radiation) acts on the cell. (2) Intracellular oxidative stress increases; the intracellular reactive oxygen species (ROS) content exceeds the antioxidative capacity of the cell (mediated mostly by an enzymatic system involving a superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)) and causes molecular damage. (3) The damage further activates the caspase-like activity, and apoptosis-like death is initiated. Simultaneously, intracellular MCs begin to be released into the extracellular environment. (4) The extracellular MCs have been significantly released from dead Microcystis cells. (5) They act on the remaining Microcystis cells, and exert extracellular roles, for example, extracellular MCs can increase the production of extracellular polysaccharides (EPS) that are involved in colony formation. Eventually, the colonial form improves the survival of the remaining cells under stressful conditions.<ref name="Programmed Cell Death-Like and Acco">{{cite journal | vauthors = Hu C, Rzymski P | title = Programmed Cell Death-Like and Accompanying Release of Microcystin in Freshwater Bloom-Forming Cyanobacterium ''Microcystis'': From Identification to Ecological Relevance | journal = Toxins | volume = 11 | issue = 12 | pages = 706 | date = December 2019 | pmid = 31817272 | pmc = 6950475 | doi = 10.3390/toxins11120706 | doi-access = free }}</ref>]]
One of the most critical processes determining cyanobacterial eco-physiology is [[cellular death]]. Evidence supports the existence of controlled cellular demise in cyanobacteria, and various forms of cell death have been described as a response to biotic and abiotic stresses. However, cell death research in cyanobacteria is a relatively young field and understanding of the underlying mechanisms and molecular machinery underpinning this fundamental process remains largely elusive.<ref name=Aguilera2021 /> However, reports on cell death of marine and freshwater cyanobacteria indicate this process has major implications for the ecology of microbial communities/<ref name="Agustí2004">{{cite journal | vauthors = Agustí S | title = Viability and niche segregation of Prochlorococcus and Synechococcus cells across the Central Atlantic Ocean. | journal = Aquatic Microbial Ecology | date = June 2004 | volume = 36 | issue = 1 | pages = 53–59 | doi = 10.3354/ame036053 | doi-access = free | hdl = 10261/86957 | hdl-access = free }}</ref><ref name="Agustí2006">{{cite journal |doi=10.1111/j.1365-2427.2006.01584.x |title=Cell death in lake phytoplankton communities |year=2006 | vauthors = Agusti S, Alou EV, Hoyer MV, Frazer TK, Canfield DE |author4-link=Thomas K. Frazer |journal=[[Freshwater Biology]] |volume=51 |issue=8 |pages=1496–1506|bibcode=2006FrBio..51.1496A }}</ref><ref name=Franklin2006>{{cite journal |doi=10.1080/09670260500505433 |title=What is the role and nature of programmed cell death in phytoplankton ecology? |year=2006 | vauthors = Franklin DJ, Brussaard CP, Berges JA |journal=European Journal of Phycology |volume=41 |issue=1 |pages=1–14 |bibcode=2006EJPhy..41....1F |doi-access=free}}</ref><ref name=Sigee2007>{{cite journal |doi=10.2216/06-69.1 |title=Patterns of cell death in freshwater colonial cyanobacteria during the late summer bloom |year=2007 | vauthors = Sigee DC, Selwyn A, Gallois P, Dean AP |journal=[[Phycologia]] |volume=46 |issue=3 |pages=284–292 |bibcode=2007Phyco..46..284S }}</ref> Different forms of cell demise have been observed in cyanobacteria under several stressful conditions,<ref name=BermanFrank2004>{{cite journal |doi=10.4319/lo.2004.49.4.0997 |title=The demise of the marine cyanobacterium, Trichodesmium SPP., via an autocatalyzed cell death pathway |year=2004 | vauthors = Berman-Frank I, Bidle KD, Haramaty L, Falkowski PG |journal=[[Limnology and Oceanography]] |volume=49 |issue=4 |pages=997–1005 |bibcode=2004LimOc..49..997B |doi-access=free}}</ref><ref name=Hu2019>{{cite journal | vauthors = Hu C, Rzymski P | title = Programmed Cell Death-Like and Accompanying Release of Microcystin in Freshwater Bloom-Forming Cyanobacterium ''Microcystis'': From Identification to Ecological Relevance | journal = Toxins | volume = 11 | issue = 12 | page = 706 | date = December 2019 | pmid = 31817272 | pmc = 6950475 | doi = 10.3390/toxins11120706 | doi-access = free }}</ref> and cell death has been suggested to play a key role in developmental processes, such as akinete and heterocyst differentiation, as well as strategy for population survival.<ref name="Programmed Cell Death-Like and Acco"/><ref>{{cite journal | vauthors = Rzymski P, Klimaszyk P, Jurczak T, Poniedziałek B | title = Oxidative Stress, Programmed Cell Death and Microcystin Release in ''Microcystis aeruginosa'' in Response to ''Daphnia'' Grazers | journal = Frontiers in Microbiology | volume = 11 | pages = 1201 | date = 2020 | pmid = 32625177 | pmc = 7311652 | doi = 10.3389/fmicb.2020.01201 | doi-access = free }}</ref><ref name="Meeks-2001">{{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 | year = 2001 | pmid = 16228364 | doi = 10.1023/A:1013840025518 | bibcode = 2001PhoRe..70...85M }}</ref><ref name=Claessen2014 /><ref name=Aguilera2021 />

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=== Cyanophages ===
{{main|Cyanophage}}
{{further|Marine viruses}}

{{multiple image |total_width=450
|caption_align = center
|image1=Cyanophages.png |caption1=[[Electron micrograph]] of [[negative-stained]] ''[[Prochlorococcus]]'' [[myovirus]]es
|image2=Structure of a Myoviridae bacteriophage 2.jpg |caption2=Typical structure of a myovirus
}}

[[Cyanophage]]s are viruses that infect cyanobacteria. Cyanophages can be found in both freshwater and marine environments.<ref>{{Cite book |title=The Ecology of Cyanobacteria | vauthors = Suttle CA |date=2000-01-01 |publisher=Springer Netherlands |isbn=9780792347354 | veditors = Whitton BA, Potts M |pages=563–589|language=en |doi=10.1007/0-306-46855-7_20 |chapter=Cyanophages and Their Role in the Ecology of Cyanobacteria}}</ref> Marine and freshwater cyanophages have [[Regular icosahedron|icosahedral]] heads, which contain double-stranded DNA, attached to a tail by connector proteins.<ref name=Suttle1993>{{Cite journal | vauthors = Suttle CA, Chan AM |year=1993 |title=Marine cyanophages infecting oceanic and coastal strains of Synechococcus: abundance, . morphology, cross-infectivity and growth characteristics |journal=[[Marine Ecology Progress Series]] |volume=92 |pages=99–109 |bibcode=1993MEPS...92...99S |doi=10.3354/meps092099 |doi-access=free}}</ref> The size of the head and tail vary among species of cyanophages.
Cyanophages, like other [[bacteriophage]]s, rely on [[Brownian motion]] to collide with bacteria, and then use receptor binding proteins to recognize cell surface proteins, which leads to adherence. Viruses with contractile tails then rely on receptors found on their tails to recognize highly conserved proteins on the surface of the host cell.<ref name="Fokine-2014">{{cite journal | vauthors = Fokine A, Rossmann MG | title = Molecular architecture of tailed double-stranded DNA phages | journal = Bacteriophage | volume = 4 | issue = 1 | pages = e28281 | date = January 2014 | pmid = 24616838 | pmc = 3940491 | doi = 10.4161/bact.28281 }}</ref>

Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in [[eutrophic]] freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to ''[[Synechococcus]]'' spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.<ref name="Proctor">{{Cite journal | vauthors = Proctor LM, Fuhrman JA |year=1990 |title=Viral mortality of marine bacteria and cyanobacteria |journal=[[Nature (journal)|Nature]] |volume=343 |issue=6253 |pages=60–62 |doi=10.1038/343060a0 |bibcode=1990Natur.343...60P }}</ref>

The first cyanophage, [[Cyanophage LPP-1|LPP-1]], was discovered in 1963.<ref name=Sarma /> Cyanophages are classified within the [[bacteriophage]] families ''[[Myoviridae]]'' (e.g. [[cyanophage AS-1|AS-1]], [[cyanophage N-1|N-1]]), ''[[Podoviridae]]'' (e.g. LPP-1) and ''[[Siphoviridae]]'' (e.g. [[cyanophage S-1|S-1]]).<ref name=Sarma>{{cite book |doi=10.1201/b14316 |title=Handbook of Cyanobacteria |date=2012 |last1=Sarma |first1=T. A. |isbn=978-1-4665-5941-7 |chapter=Cyanophages |pages=417–486 |publisher=CRC Press }}</ref>

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