Cyanobacterial morphology#Filamentous

{{see also|Prokaryotic cytoskeleton}}

Cellular functions require a well-organized and coordinated internal structure to operate effectively. Cells need to build, sustain, and sometimes modify their shape, which allows them to rapidly change their behaviour in response to external factors. During different life cycle stages, such as cell growth, cell division or cell differentiation, internal structures must dynamically adapt to the current requirements. In eukaryotes, these manifold tasks are fulfilled by the cytoskeleton: proteinaceous polymers that assemble into stable or dynamic filaments or tubules in vivo and in vitro. The eukaryotic cytoskeleton is historically divided into three classes: the actin filaments (consisting of actin monomers), the microtubules (consisting of tubulin subunits) and the intermediate filaments (IFs), although other cytoskeletal classes have been identified in recent years.{{cite journal | last=Moseley | first=James B. | title=An expanded view of the eukaryotic cytoskeleton | journal=Molecular Biology of the Cell | publisher=American Society for Cell Biology (ASCB) | volume=24 | issue=11 | year=2013 | issn=1059-1524 | doi=10.1091/mbc.e12-10-0732 | pages=1615–1618| pmid=23722945 | pmc=3667716 }}{{cite book | last1=Alberts | first1=Bruce | last2=Heald | first2=Rebecca | last3=Johnson | first3=Alexander | last4=Morgan | first4=David Owen | last5=Raff | first5=Martin C. | last6=Roberts | first6=K. | last7=Walter | first7=Peter | title=Molecular biology of the cell | publication-place=New York, NY | date=2022 | isbn=978-0-393-88482-1 | oclc=1276902141}} Only the collaborative work of all three cytoskeletal systems enables proper cell mechanics.{{cite journal | last1=Huber | first1=Florian | last2=Boire | first2=Adeline | last3=López | first3=Magdalena Preciado | last4=Koenderink | first4=Gijsje H |author4-link=Gijsje Koenderink| title=Cytoskeletal crosstalk: when three different personalities team up | journal=Current Opinion in Cell Biology | publisher=Elsevier BV | volume=32 | year=2015 | issn=0955-0674 | doi=10.1016/j.ceb.2014.10.005 | pages=39–47| pmid=25460780 | s2cid=40360166 }}

The long-lasting dogma that prokaryotes, based on their simple cell shapes, do not require cytoskeletal elements was finally abolished by the discovery of FtsZ, a prokaryotic tubulin homolog,{{cite journal | last1=Bi | first1=Erfei | last2=Lutkenhaus | first2=Joe | title=FtsZ ring structure associated with division in Escherichia coli | journal=Nature | publisher=Springer Science and Business Media LLC | volume=354 | issue=6349 | year=1991 | issn=0028-0836 | doi=10.1038/354161a0 | pages=161–164| pmid=1944597 | bibcode=1991Natur.354..161B | s2cid=4329947 }}{{cite journal | last1=de Boer | first1=Piet | last2=Crossley | first2=Robin | last3=Rothfield | first3=Lawrence | title=The essential bacterial cell-division protein FtsZ is a GTPase | journal=Nature | publisher=Springer Science and Business Media LLC | volume=359 | issue=6392 | year=1992 | issn=0028-0836 | doi=10.1038/359254a0 | pages=254–256| pmid=1528268 | bibcode=1992Natur.359..254D | s2cid=2748757 }}{{cite journal | last1=Löwe | first1=Jan | last2=Amos | first2=Linda A. | title=Crystal structure of the bacterial cell-division protein FtsZ | journal=Nature | publisher=Springer Science and Business Media LLC | volume=391 | issue=6663 | year=1998 | issn=0028-0836 | doi=10.1038/34472 | pages=203–206| pmid=9428770 | bibcode=1998Natur.391..203L | s2cid=4330857 }} and MreB, a bacterial actin homolog.{{cite journal | last1=Bork | first1=P | last2=Sander | first2=C | last3=Valencia | first3=A | title=An ATPase domain common to prokaryotic cell cycle proteins, sugar kinases, actin, and hsp70 heat shock proteins. | journal=Proceedings of the National Academy of Sciences | volume=89 | issue=16 | date=1992-08-15 | issn=0027-8424 | doi=10.1073/pnas.89.16.7290 | pages=7290–7294 | pmid=1323828 | pmc=49695 | bibcode=1992PNAS...89.7290B | doi-access=free }}{{cite journal | last1=van den Ent | first1=Fusinita | last2=Amos | first2=Linda A. | last3=Löwe | first3=Jan | title=Prokaryotic origin of the actin cytoskeleton | journal=Nature | publisher=Springer Science and Business Media LLC | volume=413 | issue=6851 | year=2001 | issn=0028-0836 | doi=10.1038/35092500 | pages=39–44| pmid=11544518 | bibcode=2001Natur.413...39V | s2cid=4427828 }} These discoveries started an intense search for other cytoskeletal proteins in bacteria and archaea which finally led to the identification of bacterial IF-like proteins such as Crescentin from Caulobacter crescentus{{cite journal | last1=Ausmees | first1=Nora | last2=Kuhn | first2=Jeffrey R | last3=Jacobs-Wagner | first3=Christine | title=The Bacterial Cytoskeleton | journal=Cell | publisher=Elsevier BV | volume=115 | issue=6 | year=2003 | issn=0092-8674 | doi=10.1016/s0092-8674(03)00935-8 | pages=705–713| pmid=14675535 | s2cid=14459851 | doi-access=free }} and even bacterial-specific cytoskeletal protein classes, including bactofilins.{{cite journal | last1=Kühn | first1=Juliane | last2=Briegel | first2=Ariane | last3=Mörschel | first3=Erhard | last4=Kahnt | first4=Jörg | last5=Leser | first5=Katja | last6=Wick | first6=Stephanie | last7=Jensen | first7=Grant J | last8=Thanbichler | first8=Martin | title=Bactofilins, a ubiquitous class of cytoskeletal proteins mediating polar localization of a cell wall synthase in Caulobacter crescentus | journal=The EMBO Journal | publisher=Wiley | volume=29 | issue=2 | date=2009-12-03 | issn=0261-4189 | doi=10.1038/emboj.2009.358 | pages=327–339| pmid=19959992 | pmc=2824468 }} Constant influx of new findings finally established that numerous prokaryotic cellular functions, including cell division, cell elongation or bacterial microcompartment segregation are governed by the prokaryotic cytoskeleton.{{cite journal | last1=Lin | first1=Lin | last2=Thanbichler | first2=Martin | title=Nucleotide-independent cytoskeletal scaffolds in bacteria | journal=Cytoskeleton | publisher=Wiley | volume=70 | issue=8 | year=2013 | issn=1949-3584 | doi=10.1002/cm.21126 | pages=409–423| pmid=23852773 | s2cid=40504066 }}{{cite journal | last1=Wagstaff | first1=James | last2=Löwe | first2=Jan | title=Prokaryotic cytoskeletons: protein filaments organizing small cells | journal=Nature Reviews Microbiology | publisher=Springer Science and Business Media LLC | volume=16 | issue=4 | date=2018-01-22 | issn=1740-1526 | doi=10.1038/nrmicro.2017.153 | pages=187–201| pmid=29355854 | s2cid=3537215 }}

Cyanobacteria are today's only known prokaryotes capable of performing oxygenic photosynthesis. Based on the presence of an outer membrane, cyanobacteria are generally considered Gram-negative bacteria. However, unlike other Gram-negative bacteria, cyanobacteria contain an unusually thick peptidoglycan (PG) layer between the inner and outer membrane, thus containing features of both Gram phenotypes.{{cite journal | last1=Videau | first1=Patrick | last2=Rivers | first2=Orion S. | last3=Ushijima | first3=Blake | last4=Oshiro | first4=Reid T. | last5=Kim | first5=Min Joo | last6=Philmus | first6=Benjamin | last7=Cozy | first7=Loralyn M. | title=Mutation of the murC and murB Genes Impairs Heterocyst Differentiation in Anabaena sp. Strain PCC 7120 | journal=Journal of Bacteriology | publisher=American Society for Microbiology | volume=198 | issue=8 | date=2016-04-15 | issn=0021-9193 | doi=10.1128/jb.01027-15 | pages=1196–1206| pmid=26811320 | pmc=4859589 }}{{cite journal | last1=Hoiczyk | first1=E | last2=Baumeister | first2=W | title=Envelope structure of four gliding filamentous cyanobacteria | journal=Journal of Bacteriology | publisher=American Society for Microbiology | volume=177 | issue=9 | year=1995 | issn=0021-9193 | doi=10.1128/jb.177.9.2387-2395.1995 | pages=2387–2395| pmid=7730269 | pmc=176896 }}{{cite journal | last1=Gumbart | first1=James C. | last2=Beeby | first2=Morgan | last3=Jensen | first3=Grant J. | last4=Roux | first4=Benoît | title=Escherichia coli Peptidoglycan Structure and Mechanics as Predicted by Atomic-Scale Simulations | journal=PLOS Computational Biology | publisher=Public Library of Science (PLoS) | volume=10 | issue=2 | date=2014-02-20 | issn=1553-7358 | doi=10.1371/journal.pcbi.1003475 | page=e1003475| pmid=24586129 | pmc=3930494 | bibcode=2014PLSCB..10E3475G | doi-access=free }} Additionally, the degree of PG crosslinking is much higher in cyanobacteria than in other Gram-negative bacteria, although teichoic acids, typically present in Gram-positive bacteria, are absent.{{cite journal | last1=Hoiczyk | first1=Egbert | last2=Hansel | first2=Alfred | title=Cyanobacterial Cell Walls: News from an Unusual Prokaryotic Envelope | journal=Journal of Bacteriology | publisher=American Society for Microbiology | volume=182 | issue=5 | year=2000 | issn=0021-9193 | doi=10.1128/jb.182.5.1191-1199.2000 | pages=1191–1199| pmid=10671437 | pmc=94402 }}

While Cyanobacteria are monophyletic,{{cite journal | last1=Schirrmeister | first1=Bettina E | last2=Antonelli | first2=Alexandre | last3=Bagheri | first3=Homayoun C | title=The origin of multicellularity in cyanobacteria | journal=BMC Evolutionary Biology | publisher=Springer Science and Business Media LLC | volume=11 | issue=1 | date=2011-02-14 | page=45 | issn=1471-2148 | doi=10.1186/1471-2148-11-45| pmid=21320320 | pmc=3271361 | doi-access=free | bibcode=2011BMCEE..11...45S }} their cellular morphologies are extremely diverse and range from unicellular species to complex cell-differentiating, multicellular species. Based on this observation, cyanobacteria have been classically divided into five subsections.{{cite journal | last1=Rippka | first1=Rosmarie | last2=Stanier | first2=Roger Y. | last3=Deruelles | first3=Josette | last4=Herdman | first4=Michael | last5=Waterbury | first5=John B. | title=Generic Assignments, Strain Histories and Properties of Pure Cultures of Cyanobacteria | journal=Microbiology | publisher=Microbiology Society | volume=111 | issue=1 | date=1979-03-01 | issn=1350-0872 | doi=10.1099/00221287-111-1-1 | pages=1–61| doi-access=free }} Subsection I cyanobacteria (Chroococcales) are unicellular and divide by binary fission or budding, whereas subsection II cyanobacteria (Pleurocapsales) are also unicellular but can undergo multiple fission events, giving rise to many small daughter cells termed baeocytes. Subsection III comprises multicellular, non-cell differentiating cyanobacteria (Oscillatoriales) and subsection IV and V cyanobacteria (Nostocales and Stigonematales) are multicellular, cell differentiating cyanobacteria that form specialized cell types in the absence of combined nitrogen (heterocysts), during unfavorable conditions (akinetes) or to spread and initiate symbiosis (hormogonia). Whereas subsections III and IV form linear cell filaments (termed trichomes) that are surrounded by a common sheath, subsection V can produce lateral branches and/or divide in multiple planes, establishing multiseriate trichomes. Considering this complex morphology, it was postulated that certain subsection V-specific (cytoskeletal) proteins could be responsible for this phenotype. However, no specific gene was identified whose distribution was specifically correlated with the cell morphology among different cyanobacterial subsections.{{cite journal | last1=Dagan | first1=Tal | last2=Roettger | first2=Mayo | last3=Stucken | first3=Karina | last4=Landan | first4=Giddy | last5=Koch | first5=Robin | last6=Major | first6=Peter | last7=Gould | first7=Sven B. | last8=Goremykin | first8=Vadim V. | last9=Rippka | first9=Rosmarie | last10=Tandeau de Marsac | first10=Nicole | last11=Gugger | first11=Muriel | last12=Lockhart | first12=Peter J. | last13=Allen | first13=John F. | last14=Brune | first14=Iris | last15=Maus | first15=Irena | last16=Pühler | first16=Alfred | last17=Martin | first17=William F. | title=Genomes of Stigonematalean Cyanobacteria (Subsection V) and the Evolution of Oxygenic Photosynthesis from Prokaryotes to Plastids | journal=Genome Biology and Evolution | publisher=Oxford University Press (OUP) | volume=5 | issue=1 | date=2012-12-07 | issn=1759-6653 | doi=10.1093/gbe/evs117 | pages=31–44| pmid=23221676 | pmc=3595030 }}{{cite journal | last1=Shih | first1=Patrick M. | last2=Wu | first2=Dongying | last3=Latifi | first3=Amel | last4=Axen | first4=Seth D. | last5=Fewer | first5=David P. | last6=Talla | first6=Emmanuel | last7=Calteau | first7=Alexandra | last8=Cai | first8=Fei | last9=Tandeau de Marsac | first9=Nicole | last10=Rippka | first10=Rosmarie | last11=Herdman | first11=Michael | last12=Sivonen | first12=Kaarina | last13=Coursin | first13=Therese | last14=Laurent | first14=Thierry | last15=Goodwin | first15=Lynne | last16=Nolan | first16=Matt | last17=Davenport | first17=Karen W. | last18=Han | first18=Cliff S. | last19=Rubin | first19=Edward M. | last20=Eisen | first20=Jonathan A. | last21=Woyke | first21=Tanja | last22=Gugger | first22=Muriel | last23=Kerfeld | first23=Cheryl A. | title=Improving the coverage of the cyanobacterial phylum using diversity-driven genome sequencing | journal=Proceedings of the National Academy of Sciences | volume=110 | issue=3 | date=2012-12-31 | issn=0027-8424 | doi=10.1073/pnas.1217107110 | pages=1053–1058 | pmid=23277585 | pmc=3549136 | doi-access=free }} Therefore, it seems more likely that differential expression of cell growth and division genes rather than the presence or absence of a single gene is responsible for the cyanobacterial morphological diversity.{{cite journal | last1=Koch | first1=Robin | last2=Kupczok | first2=Anne | last3=Stucken | first3=Karina | last4=Ilhan | first4=Judith | last5=Hammerschmidt | first5=Katrin | last6=Dagan | first6=Tal | title=Plasticity first: molecular signatures of a complex morphological trait in filamentous cyanobacteria | journal=BMC Evolutionary Biology | publisher=Springer Science and Business Media LLC | volume=17 | issue=1 | date=2017-08-31 | page=209 | issn=1471-2148 | doi=10.1186/s12862-017-1053-5| pmid=28859625 | pmc=5580265 | doi-access=free | bibcode=2017BMCEE..17..209K }}

File:Cyanobacterial cell division and cell growth mutant phenotypes.png and cell growth mutant phenotypes in Synechocystis, Synechococcus, and Anabaena. Stars indicate gene essentiality in the respective organism. While one gene can be essential in one cyanobacterial organism/morphotype, it does not necessarily mean it is essential in all other cyanobacteria. N/A indicates that no mutant phenotypes have been described. WT: wild type.{{cite journal | last1=Springstein | first1=Benjamin L. | last2=Nürnberg | first2=Dennis J. | last3=Weiss | first3=Gregor L. | last4=Pilhofer | first4=Martin | last5=Stucken | first5=Karina | title=Structural Determinants and Their Role in Cyanobacterial Morphogenesis | journal=Life | publisher=MDPI AG | volume=10 | issue=12 | date=2020-12-17 | issn=2075-1729 | doi=10.3390/life10120355 | page=355 | pmid=33348886 | pmc=7766704 | bibcode=2020Life...10..355S | doi-access=free }} Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].]]

Morphogenesis is the biological process that causes an organism to develop its shape. Cyanobacteria show a high degree of morphological diversity and can undergo a variety of cellular differentiation processes in order to adapt to certain environmental conditions. This helps them thrive in almost every habitat on Earth, ranging from freshwater to marine and terrestrial habitats, including even symbiotic interactions.{{cite book | last1=Gaysina | first1=Lira A. | last2=Saraf | first2=Aniket | last3=Singh | first3=Prashant | title=Cyanobacteria | chapter=Cyanobacteria in Diverse Habitats | publisher=Elsevier | year=2019 | pages=1–28 | doi=10.1016/b978-0-12-814667-5.00001-5| isbn=9780128146675 | s2cid=135429562 }}

One factor which can drive morphological changes in cyanobacteria is light. As cyanobacteria are bacteria that use light to fuel their energy-producing photosynthetic machinery they depend on perceiving light in order to optimize their response and to avoid harmful light that could result in the formation of reactive oxygen species and subsequently in their death.{{cite journal | last=Pospíšil | first=Pavel | title=Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress | journal=Frontiers in Plant Science | publisher=Frontiers Media SA | volume=7 | date=2016-12-26 | page=1950 | issn=1664-462X | doi=10.3389/fpls.2016.01950 | pmid=28082998 | pmc=5183610 | doi-access=free }} Optimal light conditions may be defined by quantity (irradiance), duration (day–night cycle) and wavelength (color of light). The photosynthetically usable light range of the solar spectrum is generally referred to as PAR (photosynthetically active radiation), but some cyanobacteria may expand on PAR by not only absorbing in the visible spectrum, but also the near-infrared light spectrum. This employs a variety of chlorophylls and allows phototrophic growth up to a wavelength of 750 nm.{{cite journal | doi=10.1007/s11099-018-0792-x | title=Living off the Sun: Chlorophylls, bacteriochlorophylls and rhodopsins | year=2018 | last1=Larkum | first1=A. W. D. | last2=Ritchie | first2=R. J. | last3=Raven | first3=J. A. | journal=Photosynthetica | volume=56 | pages=11–43 | s2cid=4907693 }} To sense the light across this range of wavelengths, cyanobacteria possess various photoreceptors of the phytochrome superfamily.{{cite journal | last1=Wiltbank | first1=Lisa B. | last2=Kehoe | first2=David M. | title=Diverse light responses of cyanobacteria mediated by phytochrome superfamily photoreceptors | journal=Nature Reviews Microbiology | publisher=Springer Science and Business Media LLC | volume=17 | issue=1 | date=2018-11-08 | issn=1740-1526 | doi=10.1038/s41579-018-0110-4 | pages=37–50| pmid=30410070 | s2cid=256744429 }}

Morphological plasticity, or the ability of one cell to alternate between different shapes, is a common strategy of many bacteria in response to environmental changes or as part of their normal life cycle.{{cite journal | last1=Zhu | first1=Zaichun | last2=Piao | first2=Shilong | last3=Myneni | first3=Ranga B. | last4=Huang | first4=Mengtian | last5=Zeng | first5=Zhenzhong | last6=Canadell | first6=Josep G. | last7=Ciais | first7=Philippe | last8=Sitch | first8=Stephen | last9=Friedlingstein | first9=Pierre | last10=Arneth | first10=Almut | last11=Cao | first11=Chunxiang | last12=Cheng | first12=Lei | last13=Kato | first13=Etsushi | last14=Koven | first14=Charles | last15=Li | first15=Yue | last16=Lian | first16=Xu | last17=Liu | first17=Yongwen | last18=Liu | first18=Ronggao | last19=Mao | first19=Jiafu | last20=Pan | first20=Yaozhong | last21=Peng | first21=Shushi | last22=Peñuelas | first22=Josep | last23=Poulter | first23=Benjamin | last24=Pugh | first24=Thomas A. M. | last25=Stocker | first25=Benjamin D. | last26=Viovy | first26=Nicolas | last27=Wang | first27=Xuhui | last28=Wang | first28=Yingping | last29=Xiao | first29=Zhiqiang | last30=Yang | first30=Hui | last31=Zaehle | first31=Sönke | last32=Zeng | first32=Ning | title=Greening of the Earth and its drivers | journal=Nature Climate Change | publisher=Springer Science and Business Media LLC | volume=6 | issue=8 | date=2016-04-25 | issn=1758-678X | doi=10.1038/nclimate3004 | pages=791–795| bibcode=2016NatCC...6..791Z | s2cid=7980894 | url=https://www.escholarship.org/uc/item/8mc6q011 | hdl=10871/22651 | hdl-access=free }}{{cite journal | last1=Caccamo | first1=Paul D. | last2=Brun | first2=Yves V. | title=The Molecular Basis of Noncanonical Bacterial Morphology | journal=Trends in Microbiology | publisher=Elsevier BV | volume=26 | issue=3 | year=2018 | issn=0966-842X | doi=10.1016/j.tim.2017.09.012 | pages=191–208| pmid=29056293 | pmc=5834356 }} Bacteria may alter their shape by simpler transitions from rod to coccoid (and vice versa) as in Escherichia coli,{{cite journal | last1=Lange | first1=R | last2=Hengge-Aronis | first2=R | title=Growth phase-regulated expression of bolA and morphology of stationary-phase Escherichia coli cells are controlled by the novel sigma factor sigma S | journal=Journal of Bacteriology | publisher=American Society for Microbiology | volume=173 | issue=14 | year=1991 | issn=0021-9193 | doi=10.1128/jb.173.14.4474-4481.1991 | pages=4474–4481| pmid=1648559 | pmc=208111 }} by more complex transitions while establishing multicellularity or by the development of specialized cells, structures or appendages where the population presents a pleomorphic lifestyle.{{cite journal | last=Young | first=Kevin D. | title=The Selective Value of Bacterial Shape | journal=Microbiology and Molecular Biology Reviews | publisher=American Society for Microbiology | volume=70 | issue=3 | year=2006 | issn=1092-2172 | doi=10.1128/mmbr.00001-06 | pages=660–703| pmid=16959965 | pmc=1594593 }} The precise molecular circuits that govern those morphological changes are yet to be identified, however, a so-far constant factor is that the cell shape is determined by the rigid PG sacculus which consists of glycan strands crosslinked by peptides. To grow, cells must synthesize new PG while breaking down the existent polymer to insert the newly synthesized material. How cells grow and elongate has been extensively reviewed in model organisms of both, rod-shaped{{cite journal | last1=Typas | first1=Athanasios | last2=Banzhaf | first2=Manuel | last3=Gross | first3=Carol A. | last4=Vollmer | first4=Waldemar | title=From the regulation of peptidoglycan synthesis to bacterial growth and morphology | journal=Nature Reviews Microbiology | publisher=Springer Science and Business Media LLC | volume=10 | issue=2 | date=2011-12-28 | issn=1740-1526 | doi=10.1038/nrmicro2677 | pages=123–136| pmid=22203377 | pmc=5433867 }}{{cite journal | last1=Egan | first1=Alexander J. F. | last2=Errington | first2=Jeff | last3=Vollmer | first3=Waldemar | title=Regulation of peptidoglycan synthesis and remodelling | journal=Nature Reviews Microbiology | publisher=Springer Science and Business Media LLC | volume=18 | issue=8 | date=2020-05-18 | issn=1740-1526 | doi=10.1038/s41579-020-0366-3 | pages=446–460| pmid=32424210 | s2cid=256745837 }} and coccoid bacteria.{{cite journal | last1=Pinho | first1=Mariana G. | last2=Kjos | first2=Morten | last3=Veening | first3=Jan-Willem | title=How to get (a)round: mechanisms controlling growth and division of coccoid bacteria | journal=Nature Reviews Microbiology | publisher=Springer Science and Business Media LLC | volume=11 | issue=9 | date=2013-08-16 | issn=1740-1526 | doi=10.1038/nrmicro3088 | pages=601–614| pmid=23949602 | s2cid=205498610 | url=https://pure.rug.nl/ws/files/6799095/2013NatRevMicrobiolPinho.pdf }} The molecular basis for morphological plasticity and pleomorphism in more complex bacteria, however, is slowly being elucidated as well.

Despite their morphological complexity, cyanobacteria contain all conserved and so far known bacterial morphogens. Understanding cyanobacterial morphogenesis is challenging, as there are numerous morphotypes among cyanobacterial taxa, which can also vary within a given strain during its life cycle. Changes in cellular or even trichome morphologies are tasks that would require active cell wall remodelling and thus far no genes attributed to the different morphotypes have been identified in cyanobacteria. Therefore, the most likely scenario is that genes or their products are differentially regulated during these cell morphology transitions, as it has been hypothesized for most bacteria. In multicellular cyanobacteria, division of labor between cells within a trichome is achieved by different cell programing strategies. Thus, gene regulation occurs differentially in these specific cell types [30,97,98].

Cyanobacteria present remarkable variability in terms of morphology: from unicellular and colonial to multicellular filamentous forms. Their cell size varies from less than 1 μm in diameter (picocyanobacteria) up to 100 μm (some tropical forms in the genus Oscillatoria){{cite book | last=Whitton | first=Brian A. | title=Photosynthetic Prokaryotes | chapter=Diversity, Ecology, and Taxonomy of the Cyanobacteria | publisher=Springer US | publication-place=Boston, MA | year=1992 | pages=1–51 | isbn=978-1-4757-1334-3 | doi=10.1007/978-1-4757-1332-9_1}}{{citation | last1=Schulz-Vogt | first1=Heide N | last2=Angert | first2=Esther R | last3=Garcia-Pichel | first3=Ferran | title=eLS | chapter=Giant Bacteria | publisher=Wiley | date=2007-09-28 | doi=10.1002/9780470015902.a0020371| isbn=9780470016176 }}{{cite book | last1=Jasser | first1=Iwona | last2=Callieri | first2=Cristiana | title=Handbook of Cyanobacterial Monitoring and Cyanotoxin Analysis | chapter=Picocyanobacteria | publisher=John Wiley & Sons, Ltd | publication-place=Chichester, UK | date=2017-02-11 | pages=19–27 | doi=10.1002/9781119068761.ch3| isbn=9781119068761 }}

Filamentous forms exhibit functional cell differentiation such as heterocysts (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.{{cite journal |doi = 10.1038/nrmicro3178|title = Bacterial solutions to multicellularity: A tale of biofilms, filaments and fruiting bodies|year = 2014|last1 = Claessen|first1 = Dennis|last2 = Rozen|first2 = Daniel E.|last3 = Kuipers|first3 = Oscar P.|last4 = Søgaard-Andersen|first4 = Lotte|last5 = Van Wezel|first5 = Gilles P.|journal = Nature Reviews Microbiology|volume = 12|issue = 2|pages = 115–124|pmid = 24384602|hdl = 11370/0db66a9c-72ef-4e11-a75d-9d1e5827573d|s2cid = 20154495|url = https://research.rug.nl/en/publications/bacterial-solutions-to-multicellularity(0db66a9c-72ef-4e11-a75d-9d1e5827573d).html|hdl-access = free}}{{cite journal |doi = 10.1111/mmi.12506|title = Branching and intercellular communication in the Section V cyanobacterium Mastigocladus laminosus, a complex multicellular prokaryote|year = 2014|last1 = Nürnberg|first1 = Dennis J.|last2 = Mariscal|first2 = Vicente|last3 = Parker|first3 = Jamie|last4 = Mastroianni|first4 = Giulia|last5 = Flores|first5 = Enrique|last6 = Mullineaux|first6 = Conrad W.|journal = Molecular Microbiology|volume = 91|issue = 5|pages = 935–949|pmid = 24383541|s2cid = 25479970|hdl = 10261/99110|hdl-access = free}}{{cite journal |doi = 10.1093/femsre/fuw029|title = The multicellular nature of filamentous heterocyst-forming cyanobacteria|year = 2016|last1 = Herrero|first1 = Antonia|last2 = Stavans|first2 = Joel|last3 = Flores|first3 = Enrique|journal = FEMS Microbiology Reviews|volume = 40|issue = 6|pages = 831–854|pmid = 28204529|hdl = 10261/140753|hdl-access = free}}{{cite journal |doi = 10.3389/fmicb.2021.631654|doi-access = free|title = Cell Death in Cyanobacteria: Current Understanding and Recommendations for a Consensus on Its Nomenclature|year = 2021|last1 = Aguilera|first1 = Anabella|last2 = Klemenčič|first2 = Marina|last3 = Sueldo|first3 = Daniela J.|last4 = Rzymski|first4 = Piotr|last5 = Giannuzzi|first5 = Leda|last6 = Martin|first6 = María Victoria|journal = Frontiers in Microbiology|volume = 12|page = 631654|pmid = 33746925|pmc = 7965980}} 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere.{{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 = 222–33 | date = April 2014 | pmid = 24533832 | doi = 10.1111/mmi.12552 | s2cid = 37479716 | doi-access = free }}{{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 | 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 | date = May 2017 | pmid = 28242721 | pmc = 5388816 | doi = 10.1128/JB.00075-17 | pages=e00075–17}} 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.

{{multiple image

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| footer = Drawings by Allan Pentecost

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| caption1 = Unicellular and colonial cyanobacteria
scale bars about 10 μm

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| caption2 = Simple cyanobacterial filaments Nostocales, Oscillatoriales and Spirulinales

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| caption3 = Branched forms
Tolypothrix, Scytonema, Stigonema and Fischerella

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| caption4 = Cyanobacteria associated with tufa
Schizothrix calcicola, Gloeocapsa, Coccochloris, Microcoleus vaginatus and Rivularia

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In aquatic habitats, unicellular cyanobacteria are considered as an important group regarding abundance, diversity, and ecological character.{{cite book | last1=Dvořák | first1=Petr | last2=Casamatta | first2=Dale A. | last3=Hašler | first3=Petr | last4=Jahodářová | first4=Eva | last5=Norwich | first5=Alyson R. | last6=Poulíčková | first6=Aloisie | pages=3–46 | title=Modern Topics in the Phototrophic Prokaryotes | chapter=Diversity of the Cyanobacteria | publisher=Springer International Publishing | publication-place=Cham | year=2017 | isbn=978-3-319-46259-2 | doi=10.1007/978-3-319-46261-5_1}} Unicellular cyanobacteria have spherical, ovoid, or cylindrical cells that may aggregate into irregular or regular colonies bound together by the mucous matrix (mucilage) secreted during the growth of the colony.{{cite book | last1=Chorus | first1=Ingrid | last2=Bartram | first2=Jamie | title=Toxic cyanobacteria in water : a guide to their public health consequences, monitoring, and management | publisher=E & FN Spon | publication-place=London | date=1999 | isbn=0-419-23930-8 | oclc=40395794}} Based on the species, the number of cells in each colony may vary from two to several thousand.

Each individual cell (each single cyanobacterium) typically has a thick, gelatinous cell wall.{{Cite book|url={{google books |plainurl=y |id=xNQE_89dat8C|page=72}}|title=Text Book of Botany Diversity of Microbes And Cryptogams|last=Singh|publisher=Rastogi Publications|isbn=978-8171338894}} They lack flagella, but hormogonia of some species can move about by gliding along surfaces.{{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}}

File:Merismopedia.jpg| Merismopedia forms rectangular colonies held together by a mucilaginous matrix. Species in this genus divide in only two directions, creating a characteristic grid-like pattern arranged in rows and flats.{{cite journal|last1=Palinska|first1=Katarzyna A.|last2=Liesack|first2=Werner|last3=Rhiel|first3=Erhard|last4=Krumbein|first4=W. E.|title=Phenotype variability of identical genotypes: the need for a combined approach in cyanobacterial taxonomy demonstrated on Merismopedia-like isolates|journal=Archives of Microbiology|date=17 October 1996|volume=166|issue=4|pages=224–233|doi=10.1007/s002030050378|pmid=8824145 |bibcode=1996ArMic.166..224P |s2cid=3022844 }}

File:CyanobacteriaColl1.jpg| Colonies of Nostoc pruniforme "jelly balls"

File:Colonial-cyanobacteria-of-the-Stratonostoc-species-on-the-coast-of-the-Barguzinsky-Bay-of-Lake-Baikal.jpg|Colonial cyanobacteria Stratonostoc

File:Gloeotrichia in Sytox.jpg|Ball-shaped colony of Gloeotrichia echinulata

File:Lyngbya majuscula.jpg| Cyanobacterial colony of Lyngbya majuscula

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File:Filamentous cyanobacteria structure of Oscillatoria lutea.jpg| Example of filamentous cyanobacteria structure (Oscillatoria lutea) showing a reticulate pattern{{hsp}}

{{see also|Segmented filamentous bacteria|Bacterial morphological plasticity}}

Some filamentous species can differentiate into several different cell types:

• vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions
• akinetes – climate-resistant spores that may form when environmental conditions become harsh
• thick-walled heterocysts – which contain the enzyme nitrogenase vital for nitrogen fixation{{cite journal | vauthors = Meeks JC, Elhai J, Thiel T, Potts M, Larimer F, Lamerdin J, Predki P, Atlas R | s2cid = 8752382 | 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 }}{{cite journal | vauthors = Golden JW, Yoon HS | title = Heterocyst formation in Anabaena | journal = Current Opinion in Microbiology | volume = 1 | issue = 6 | pages = 623–9 | date = December 1998 | pmid = 10066546 | doi=10.1016/s1369-5274(98)80106-9}}{{cite journal | vauthors = Fay P | title = Oxygen relations of nitrogen fixation in cyanobacteria | journal = Microbiological Reviews | volume = 56 | issue = 2 | pages = 340–73 | date = June 1992 | pmid = 1620069 | pmc=372871| doi = 10.1128/MMBR.56.2.340-373.1992 }} in an anaerobic environment due to its sensitivity to oxygen.

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 vesicles, as in archaea.{{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 }} These vesicles are not organelles as such. They are not bounded by lipid membranes but by a protein sheath.

File:Microphotographs of bundle-forming filamentous cyanobacteria.png cf. calcicola G: S. cf. calcicola H: S. cf. c alcicola
Scale bar {{=}}10 μm}}]]

File:Anabaena sperica2.jpg| Anabaena sperica

File:Necklace of Mermaid.tif| Anabaena is used as a model organism to study simple vision{{cite journal|last1=Schapiro|first1=Igor|title=Ultrafast photochemistry of Anabaena Sensory Rhodopsin: Experiment and theory|journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics|date=May 2014|volume=1837|issue=5|pages=589–597|doi=10.1016/j.bbabio.2013.09.014|pmid=24099700|doi-access=free}}

File:Cyanobacteria.jpg| Helical filaments of cyanobacteria

File:Dolichospermum sp.cropped-brighter.jpg| Helical filament from Dolichospermum

File:Lyngbya.jpg| Lyngbya species form long, unbranching filaments inside rigid mucilaginous sheaths which can form tangles or mats, intermixed with other phytoplankton species

{{clear left}}

File:Cyanobacteriabranchedforms026 Fischerella.jpg| Fischerella

File:Fischerella thermalis.png| True branching phenotype of a Fischerella thermalis colony

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Heterocysts are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale, and Anabaena sphaerica.{{Cite web | author= Basic Biology | date= 18 March 2016 | title= Bacteria | url= https://basicbiology.net/micro/microorganisms/bacteria}} They fix nitrogen from atmospheric N₂ using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis.{{cite book|last1=Wolk|first1=C. Peter |last2=Ernst |first2= Annaliese |last3=Elhai|first3= Jeff|chapter=Heterocyst Metabolism and Development |title=The Molecular Biology of Cyanobacteria|year=1994|pages=769–823|doi=10.1007/978-94-011-0227-8_27 |isbn=978-0-7923-3273-2 |series=Advances in Photosynthesis and Respiration | editor=Donald A. Bryant }}

File:Modeling filamentous cyanobacteria.tif Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].}} Model components: (A) Trichomes are modeled as thin flexible rods that are discretized into sequences of 50 μm edges. Each edge is loaded with a linear spring. (B) The local bending moment is a function of the radius of curvature. (C) Trichomes can glide along their long axis and reverse their direction of movement photophobically. (D) Trichome collisions are defined between edge-vertex pairs. A vertex that penetrates an edge's volume is repulsed by equal and opposite forces between the pair.]]

{{see also|Cyanobacterial motility#Filamentous cyanobacteria}}

Cyanobacteria are ubiquitous, finding habitats in most water bodies and in extreme environments such as the polar regions, deserts, brine lakes and hot springs.{{cite book |doi = 10.1016/S0070-4571(08)71140-3| chapter=Chapter 6.2 Microbiology and Morphogenesis of Columnar Stromatolites (Conophyton, Vacerrilla) from Hot Springs in Yellowstone National Park | title=Stromatolites | series=Developments in Sedimentology | year=1976 | last1=Walter | first1=M.R. | last2=Bauld | first2=J. | last3=Brock | first3=T.D. | volume=20 | pages=273–310 | isbn=9780444413765 }}{{cite journal |doi = 10.1669/0883-1351(2002)017<0084:CSFGSN>2.0.CO;2| issn=0883-1351 | year=2002 | volume=17 | page=84 | title=Coniform Stromatolites from Geothermal Systems, North Island, New Zealand | last1=Jones | first1=B. | last2=Renaut | first2=R. W. | last3=Rosen | first3=M. R. | last4=Ansdell | first4=K. M. | journal=PALAIOS | issue=1 | bibcode=2002Palai..17...84J | s2cid=130120737 }}{{cite journal |doi = 10.2216/i0031-8884-22-4-355.1| title=Distribution, species composition and morphology of algal mats in Antarctic dry valley lakes | year=1983 | last1=Wharton | first1=Robert A. | last2=Parker | first2=Bruce C. | last3=Simmons | first3=George M. | journal=Phycologia | volume=22 | issue=4 | pages=355–365 | bibcode=1983Phyco..22..355W }} They have also evolved surprisingly complex collective behaviours that lie at the boundary between single-celled and multicellular life. For example, filamentous cyanobacteria live in long chains of cells that bundle together into larger structures including biofilms, biomats and stromatolites.{{cite book |doi = 10.1007/978-94-007-3855-3| title=Ecology of Cyanobacteria II | year=2012 | isbn=978-94-007-3854-6 | s2cid=46736903 | editor-last1=Whitton | editor-first1=Brian A }}{{cite book |doi = 10.1007/978-94-007-3855-3_4| chapter=Cyanobacterial Mats and Stromatolites | title=Ecology of Cyanobacteria II | year=2012 | last1=Stal | first1=Lucas J. | pages=65–125 | isbn=978-94-007-3854-6 }} These large colonies provide a rigid, stable and long-term environment for their communities of bacteria. In addition, cyanobacteria-based biofilms can be used as bioreactors to produce a wide range of chemicals, including biofuels like biodiesel and ethanol.{{cite journal |doi = 10.1002/btpr.2835 |title = Cyanobacteria as an eco-friendly resource for biofuel production: A critical review |year = 2019 |last1 = Farrokh |first1 = Parisa |last2 = Sheikhpour |first2 = Mojgan |last3 = Kasaeian |first3 = Alibakhsh |last4 = Asadi |first4 = Hassan |last5 = Bavandi |first5 = Roya |journal = Biotechnology Progress |volume = 35 |issue = 5 |pages = e2835 |pmid = 31063628 |s2cid = 147705730 }} However, despite their importance to the history of life on Earth, and their commercial and environmental potentials, there remain basic questions of how filamentous cyanobacteria move, respond to their environment and self-organize into collective patterns and structures.{{cite journal | last1=Faluweki | first1=Mixon K. | last2=Goehring | first2=Lucas | title=Structural mechanics of filamentous cyanobacteria | journal=Journal of the Royal Society Interface | publisher=The Royal Society | volume=19 | issue=192 | year=2022 | issn=1742-5662 | doi=10.1098/rsif.2022.0268| pmid=35892203 | pmc=9326267 }} 50px Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

All known cyanobacteria lack flagella;{{cite journal |doi = 10.1099/00221287-111-1-1| title=Generic Assignments, Strain Histories and Properties of Pure Cultures of Cyanobacteria | year=1979 | last1=Rippka | first1=Rosmarie | last2=Stanier | first2=Roger Y. | last3=Deruelles | first3=Josette | last4=Herdman | first4=Michael | last5=Waterbury | first5=John B. | journal=Microbiology | volume=111 | pages=1–61 | doi-access=free }} however, many filamentous species move on surfaces by gliding, a form of locomotion where no physical appendages are seen to aid movement.{{cite journal |doi = 10.1007/s002030000187| title=Gliding motility in cyanobacteria: Observations and possible explanations | year=2000 | last1=Hoiczyk | first1=E. | journal=Archives of Microbiology | volume=174 | issue=1–2 | pages=11–17 | pmid=10985737 | bibcode=2000ArMic.174...11H | s2cid=9927312 }} The actual mechanism behind gliding is not fully understood, although over a century has elapsed since its discovery.Hansgirg A. (1883) "Bemerkungen über die Bewegungen der Oscillarien". Bot. Ztg., 41: 831.Drews G. (1959) "Beitröge zur Kenntnis der phototaktischen Reaktionen der Cyanophyceen". Arch. Protistenk. 104: 389–430. One theory suggests that gliding motion in cyanobacteria is mediated by the continuous secretion of polysaccharides through pores on individual cells.{{cite journal |doi = 10.15281/jplantres1887.64.14| title=Secretion of the slime substance in Oscillatoria in relation to its movement | year=1951 | last1=Hosoi | first1=Akimitsu | journal=Shokubutsugaku Zasshi | volume=64 | issue=751–752 | pages=14–17 | doi-access=free }}{{cite journal |doi = 10.1007/BF01666380| title=Mucilage secretion and the movements of blue-green algae | year=1968 | last1=Walsby | first1=A. E. | journal=Protoplasma | volume=65 | issue=1–2 | pages=223–238 | s2cid=20310025 }}{{cite journal |doi = 10.1016/S0960-9822(07)00487-3| title=The junctional pore complex, a prokaryotic secretion organelle, is the molecular motor underlying gliding motility in cyanobacteria | year=1998 | last1=Hoiczyk | first1=Egbert | last2=Baumeister | first2=Wolfgang | journal=Current Biology | volume=8 | issue=21 | pages=1161–1168 | pmid=9799733 | s2cid=14384308 | doi-access=free | bibcode=1998CBio....8.1161H }} Another theory suggests that gliding motion involves the use of type IV pili, polymeric assemblies of the protein pilin,{{cite journal |doi = 10.1038/nrmicro885| title=Type IV pilus structure and bacterial pathogenicity | year=2004 | last1=Craig | first1=Lisa | last2=Pique | first2=Michael E. | last3=Tainer | first3=John A. | journal=Nature Reviews Microbiology | volume=2 | issue=5 | pages=363–378 | pmid=15100690 | s2cid=10654430 }} as the driving engines of motion.{{cite journal |doi = 10.1128/JB.01927-06| title=Molecular Analysis of Genes in Nostoc punctiforme Involved in Pilus Biogenesis and Plant Infection | year=2007 | last1=Duggan | first1=Paula S. | last2=Gottardello | first2=Priscila | last3=Adams | first3=David G. | journal=Journal of Bacteriology | volume=189 | issue=12 | pages=4547–4551 | pmid=17416648 | pmc=1913353 }}{{cite journal |doi = 10.1111/mmi.12552| title=Genetic characterization of thehmplocus, a chemotaxis-like gene cluster that regulates hormogonium development and motility in Nostoc punctiforme | year=2014 | last1=Risser | first1=Douglas D. | last2=Chew | first2=William G. | last3=Meeks | first3=John C. | journal=Molecular Microbiology | volume=92 | issue=2 | pages=222–233 | pmid=24533832 | s2cid=37479716 | doi-access=free }}{{cite journal |doi = 10.1111/mmi.13205| title=Evidence that a modified type IV pilus-like system powers gliding motility and polysaccharide secretion in filamentous cyanobacteria | year=2015 | last1=Khayatan | first1=Behzad | last2=Meeks | first2=John C. | last3=Risser | first3=Douglas D. | journal=Molecular Microbiology | volume=98 | issue=6 | pages=1021–1036 | pmid=26331359 | s2cid=8749419 | url=http://www.escholarship.org/uc/item/3vb402c1 | doi-access=free }} However, it is not clear how the action of these pili would lead to motion, with some suggesting they retract,{{cite journal |doi = 10.1099/mic.0.000064 |title = PilB localization correlates with the direction of twitching motility in the cyanobacterium Synechocystis sp. PCC 6803 |year = 2015 |last1 = Schuergers |first1 = Nils |last2 = Nürnberg |first2 = Dennis J. |last3 = Wallner |first3 = Thomas |last4 = Mullineaux |first4 = Conrad W. |last5 = Wilde |first5 = Annegret |journal = Microbiology |volume = 161 |issue = 5 |pages = 960–966 |pmid = 25721851 |doi-access = free }} while others suggest they push, to generate forces. Other scholars have suggested surface waves generated by the contraction of a fibril layer as the mechanism behind gliding motion in Oscillatoria.{{cite journal |doi = 10.1038/2251163a0| title=Gliding in a Blue–Green Alga: A Possible Mechanism | year=1970 | last1=Halfen | first1=Lawrence N. | last2=Castenholz | first2=Richard W. | journal=Nature | volume=225 | issue=5238 | pages=1163–1165 | pmid=4984867 | bibcode=1970Natur.225.1163H | s2cid=10399610 }}{{cite journal |doi = 10.1111/j.1529-8817.1971.tb01492.x| title=Gliding Motility in the Blue-Green Alga Oscillatoria Princeps 1 | year=1971 | last1=Halfen | first1=Lawrence N. | last2=Castenholz | first2=Richard W. | journal=Journal of Phycology | volume=7 | issue=2 | pages=133–145 | bibcode=1971JPcgy...7..133H | s2cid=86115246 }} Recent work also suggests that shape fluctuations and capillary forces could be involved in gliding motion.{{cite journal |doi = 10.1073/pnas.1914678116| title=Mechanisms for bacterial gliding motility on soft substrates | year=2019 | last1=Tchoufag | first1=Joël | last2=Ghosh | first2=Pushpita | last3=Pogue | first3=Connor B. | last4=Nan | first4=Beiyan | last5=Mandadapu | first5=Kranthi K. | journal=Proceedings of the National Academy of Sciences | volume=116 | issue=50 | pages=25087–25096 | pmid=31767758 | pmc=6911197 | arxiv=1807.07529 | bibcode=2019PNAS..11625087T | doi-access=free }}

Through collective interaction, filamentous cyanobacteria self-organize into colonies or biofilms, symbiotic communities found in a wide variety of ecological niches. Their larger-scale collective structures are characterized by diverse shapes including bundles, vortices and reticulate patterns.{{cite journal |doi = 10.1111/j.1472-4669.2010.00235.x| title=Undirected motility of filamentous cyanobacteria produces reticulate mats | year=2010 | last1=Shepard | first1=R. N. | last2=Sumner | first2=D. Y. | journal=Geobiology | volume=8 | issue=3 | pages=179–190 | pmid=20345889 | bibcode=2010Gbio....8..179S | s2cid=24452272 | doi-access=free }}{{cite journal |doi = 10.1016/j.earscirev.2016.01.005| title=Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes | year=2016 | last1=Davies | first1=Neil S. | last2=Liu | first2=Alexander G. | last3=Gibling | first3=Martin R. | last4=Miller | first4=Randall F. | journal=Earth-Science Reviews | volume=154 | pages=210–246 | bibcode=2016ESRv..154..210D | s2cid=56345018 | doi-access=free | hdl=1983/bd67cb45-b022-4db0-be3d-b2977d2b81ab | hdl-access=free }} Similar patterns have been observed in fossil records.{{cite journal |doi = 10.1038/nature04764| title=Stromatolite reef from the Early Archaean era of Australia | year=2006 | last1=Allwood | first1=Abigail C. | last2=Walter | first2=Malcolm R. | last3=Kamber | first3=Balz S. | last4=Marshall | first4=Craig P. | last5=Burch | first5=Ian W. | journal=Nature | volume=441 | issue=7094 | pages=714–718 | pmid=16760969 | bibcode=2006Natur.441..714A | s2cid=4417746 }}{{cite journal |doi = 10.2307/3515333| jstor=3515333 | title=Late Archean Calcite-Microbe Interactions: Two Morphologically Distinct Microbial Communities That Affected Calcite Nucleation Differently | last1=Sumner | first1=Dawn Y. | journal=PALAIOS | year=1997 | volume=12 | issue=4 | pages=302–318 | bibcode=1997Palai..12..302S }} For filamentous cyanobacteria, the mechanics of the filaments is known to contribute to self-organization, for example in determining how one filament will bend when in contact with other filaments or obstacles.{{cite journal |doi = 10.3390/life4030433| doi-access=free | title=A Model of Filamentous Cyanobacteria Leading to Reticulate Pattern Formation | year=2014 | last1=Tamulonis | first1=Carlos | last2=Kaandorp | first2=Jaap | journal=Life | volume=4 | issue=3 | pages=433–456 | pmid=25370380 | pmc=4206854 | bibcode=2014Life....4..433T }} Further, biofilms and biomats show some remarkably conserved macro-mechanical properties, typically behaving as viscoelastic materials with a relaxation time of about 20 min.{{cite journal |doi = 10.1103/PhysRevLett.93.098102| title=Commonality of Elastic Relaxation Times in Biofilms | year=2004 | last1=Shaw | first1=T. | last2=Winston | first2=M. | last3=Rupp | first3=C. J. | last4=Klapper | first4=I. | last5=Stoodley | first5=P. | journal=Physical Review Letters | volume=93 | issue=9 | page=098102 | pmid=15447143 | bibcode=2004PhRvL..93i8102S | url=https://scholarworks.montana.edu/xmlui/handle/1/13369 }}

Cyanobacteria have strict light requirements. Too little light can result in insufficient energy production, and in some species may cause the cells to resort to heterotrophic respiration. Too much light can inhibit the cells, decrease photosynthesis efficiency and cause damage by bleaching. UV radiation is especially deadly for cyanobacteria, with normal solar levels being significantly detrimental for these microorganisms in some cases.{{cite journal |doi = 10.1371/journal.pone.0022084|title = Modeling Filamentous Cyanobacteria Reveals the Advantages of Long and Fast Trichomes for Optimizing Light Exposure|year = 2011|last1 = Tamulonis|first1 = Carlos|last2 = Postma|first2 = Marten|last3 = Kaandorp|first3 = Jaap|journal = PLOS ONE|volume = 6|issue = 7|pages = e22084|pmid = 21789215|pmc = 3138769| bibcode=2011PLoSO...622084T |doi-access = free}}{{cite journal |doi = 10.1111/j.1574-6941.1993.tb00026.x|title = Effects of tropical solar radiation on the motility of filamentous cyanobacteria|year = 1993|last1 = Donkor|first1 = Victoria A.|last2 = Amewowor|first2 = Damina H.A.K.|last3 = Hã¤Der|first3 = Donat-P.|journal = FEMS Microbiology Ecology|volume = 12|issue = 2|pages = 143–147|doi-access = free| bibcode=1993FEMME..12..143D }}

Filamentous cyanobacteria that live in microbial mats often migrate vertically and horizontally within the mat in order to find an optimal niche that balances their light requirements for photosynthesis against their sensitivity to photodamage. For example, the filamentous cyanobacteria Oscillatoria sp. and Spirulina subsalsa found in the hypersaline benthic mats of Guerrero Negro, Mexico migrate downwards into the lower layers during the day in order to escape the intense sunlight and then rise to the surface at dusk.{{cite journal |doi = 10.1128/aem.60.5.1500-1511.1994|title = Diel Migrations of Microorganisms within a Benthic, Hypersaline Mat Community|year = 1994|last1 = Garcia-Pichel|first1 = Ferran|last2 = Mechling|first2 = Margaret|last3 = Castenholz|first3 = Richard W.|journal = Applied and Environmental Microbiology|volume = 60|issue = 5|pages = 1500–1511|pmid = 16349251|pmc = 201509| bibcode=1994ApEnM..60.1500G }} In contrast, the population of Microcoleus chthonoplastes found in hypersaline mats at Salin-de-Giraud, Camargue, France migrate to the upper layer of the mat during the day and are spread homogenously through the mat at night.{{cite journal |doi = 10.1111/j.1574-6941.2006.00124.x|title = Vertical migration of phototrophic bacterial populations in a hypersaline microbial mat from Salins-de-Giraud (Camargue, France)|year = 2006|last1 = Fourã§Ans|first1 = Aude|last2 = Solã©|first2 = Antoni|last3 = Diestra|first3 = Ella|last4 = Ranchou-Peyruse|first4 = Anthony|last5 = Esteve|first5 = Isabel|last6 = Caumette|first6 = Pierre|last7 = Duran|first7 = Robert|journal = FEMS Microbiology Ecology|volume = 57|issue = 3|pages = 367–377|pmid = 16907751|doi-access = free| bibcode=2006FEMME..57..367F }} An in vitro experiment using P. uncinatum also demonstrated this species' tendency to migrate in order to avoid damaging radiation. These migrations are usually the result of some sort of photomovement, although other forms of taxis can also play a role.{{cite journal |doi = 10.1128/aem.53.9.2142-2150.1987|title = Diel Vertical Movements of the Cyanobacterium Oscillatoria terebriformis in a Sulfide-Rich Hot Spring Microbial Mat|year = 1987|last1 = Richardson|first1 = Laurie L.|last2 = Castenholz|first2 = Richard W.|journal = Applied and Environmental Microbiology|volume = 53|issue = 9|pages = 2142–2150|pmid = 16347435|pmc = 204072| bibcode=1987ApEnM..53.2142R }}

Many species of cyanobacteria are capable of gliding. Gliding is a form of cell movement that differs from crawling or swimming in that it does not rely on any obvious external organ or change in cell shape and it occurs only in the presence of a substrate.{{cite journal |doi = 10.1146/annurev.micro.55.1.49|title = Bacterial Gliding Motility: Multiple Mechanisms for Cell Movement over Surfaces|year = 2001|last1 = McBride|first1 = Mark J.|journal = Annual Review of Microbiology|volume = 55|pages = 49–75|pmid = 11544349}}{{cite journal |doi = 10.1146/annurev.mi.35.100181.002011|title = Taxonomy of the Gliding Bacteria|year = 1981|last1 = Reichenbach|first1 = H.|journal = Annual Review of Microbiology|volume = 35|pages = 339–364|pmid = 6794424}} Gliding in filamentous cyanobacteria appears to be powered by a "slime jet" mechanism, in which the cells extrude a gel that expands quickly as it hydrates providing a propulsion force,{{cite journal |doi = 10.1016/S0960-9822(07)00487-3|title = The junctional pore complex, a prokaryotic secretion organelle, is the molecular motor underlying gliding motility in cyanobacteria|year = 1998|last1 = Hoiczyk|first1 = Egbert|last2 = Baumeister|first2 = Wolfgang|journal = Current Biology|volume = 8|issue = 21|pages = 1161–1168|pmid = 9799733|s2cid = 14384308|doi-access = free| bibcode=1998CBio....8.1161H }}{{cite journal |doi = 10.1007/s002030000187|title = Gliding motility in cyanobacteria: Observations and possible explanations|year = 2000|last1 = Hoiczyk|first1 = E.|journal = Archives of Microbiology|volume = 174|issue = 1–2|pages = 11–17|pmid = 10985737| bibcode=2000ArMic.174...11H |s2cid = 9927312}} although some unicellular cyanobacteria use type IV pili for gliding.{{cite journal |doi = 10.1073/pnas.96.6.3188|title = The role of an alternative sigma factor in motility and pilus formation in the cyanobacterium Synechocystis sp. Strain PCC6803|year = 1999|last1 = Bhaya|first1 = D.|last2 = Watanabe|first2 = N.|last3 = Ogawa|first3 = T.|last4 = Grossman|first4 = A. R.|journal = Proceedings of the National Academy of Sciences|volume = 96|issue = 6|pages = 3188–3193|pmid = 10077659|pmc = 15917|bibcode = 1999PNAS...96.3188B|doi-access = free}} Individual cells in a trichome have two sets of pores for extruding slime. Each set is organized in a ring at the cell septae and extrudes slime at an acute angle.{{cite journal |doi = 10.1128/jb.177.9.2387-2395.1995|title = Envelope structure of four gliding filamentous cyanobacteria|year = 1995|last1 = Hoiczyk|first1 = E.|last2 = Baumeister|first2 = W.|journal = Journal of Bacteriology|volume = 177|issue = 9|pages = 2387–2395|pmid = 7730269|pmc = 176896}} The sets extrude slime in opposite directions and so only one set is likely to be activated during gliding. An alternative hypothesis is that the cells use contractive elements that produce undulations running over the surface inside the slime tube like an earthworm.{{cite journal |doi = 10.1111/j.1529-8817.1971.tb01492.x|title = Gliding Motility in the Blue-Green Alga Oscillatoria Princeps 1|year = 1971|last1 = Halfen|first1 = Lawrence N.|last2 = Castenholz|first2 = Richard W.|journal = Journal of Phycology|volume = 7|issue = 2|pages = 133–145| bibcode=1971JPcgy...7..133H |s2cid = 86115246}} The trichomes rotate in a spiral fashion, the angle of which corresponds with the

pitch angle of Castenholz's contractile trichomes.

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File:Filamentous cyanobacteria under confocal fluorescence imaging.jpg appear as long thin curved filaments. (b) When rendered inactive, for example by being briefly cooled, the same filaments adopt a more random shape. (c) Under higher magnification O. lutea is seen to be composed of one-cell-wide strands of connected cells.]]

File:Oscillatoria filaments.jpg are capable of a waving motion}}]]

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The cells appear to coordinate their gliding direction by an electrical potential that establishes polarity in the trichomes, and thus establishes a "head" and the "tail".{{cite journal |doi = 10.1093/oxfordjournals.pcp.a076487|title = Enhanced Model for Photophobic Responses of the Blue-Green Alga, Phormidium uncinatum|journal = Plant and Cell Physiology|year = 1982}} Trichomes usually reverse their polarity randomly with an average period on the order of minutes to hours.{{cite journal |doi = 10.1111/j.1751-1097.1987.tb04745.x|title = EFFECTS OF UV-B IRRADIATION ON PHOTOMOVEMENT IN THE DESMID, Cosmarium cucumis|year = 1987|last1 = Häder|first1 = Donat-P.|journal = Photochemistry and Photobiology|volume = 46|pages = 121–126|s2cid = 97100233}}{{cite journal |doi = 10.1111/j.1574-6968.1985.tb00998.x|title = A one-instant mechanism of phototaxis in the cyanobacterium Phormidium uncinatum|year = 1985|last1 = Gabai|first1 = V.L.|journal = FEMS Microbiology Letters|volume = 30|issue = 1–2|pages = 125–129|doi-access = free}} Many species also form a semi-rigid sheath that is left behind as a hollow tube as the trichome moves forward. When the trichome reverses direction, it can move back into the sheath or break out.Häder, D.P. (1987) "Photomovement". The Cyanobacteria: 325-345.

Oscillatoria is a genus of filamentous cyanobacterium named after the oscillation in its movement. Filaments in colonies slide back and forth against each other until the whole mass is reoriented to its light source. Oscillatoria is mainly blue-green or brown-green and is commonly found in watering-troughs. It reproduces by fragmentation forming long filaments of cells which can break into fragments called hormogonia. The hormogonia can then grow into new, longer filaments.

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• Bacterial cellular morphologies
• Colonial morphology

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Category:Cyanobacteria