Cyanobacteria 129618 225118773 2008-07-11T23:39:05Z 98.217.172.172 Fixed Grammar {{Taxobox | color = lightgrey | name = Cyanobacteria | image = Anabaena_sperica.jpg | image_width = 250px | image_caption = ''[[Anabaena|Anabaena sphaerica]]'' | domain = [[Bacteria]] | phylum = '''Cyanobacteria''' | subdivision_ranks = Orders | subdivision = The taxonomy is currently under revision.<ref> {{cite journal |author=Ahoren Oren |year=2004 |title=A proposal for further integration of the cyanobacteria under the Bacteriological Code |journal=Int. J. Syst. Evol. Microbiol. |volume=54 |pages=1895–1902 |doi=10.1099/ijs.0.03008-0 |pmid=15388760 }}</ref> }} '''Cyanobacteria''', also known as '''blue-green algae''', '''blue-green bacteria''' or '''Cyanophyta''', is a [[phylum (biology)|phylum]] of [[bacteria]] that obtain their energy through [[photosynthesis]]. The name "cyanobacteria" comes from the color of the bacteria ([[Greek language|Greek]]: ''κυανός (kyanós)'' = blue). They are a significant component of the marine [[nitrogen cycle]] and an important [[autotroph|primary producer]] in many areas of the ocean, but are also found on land. [[Stromatolite]]s of [[fossil]]ized oxygen-producing cyanobacteria have been found from 2.8 billion years ago.<ref>{{cite journal |author=Olson JM |title=Photosynthesis in the Archean era |journal=Photosyn. Res. |volume=88 |issue=2 |pages=109–17 |year=2006 |pmid=16453059 |doi=10.1007/s11120-006-9040-5}}</ref> The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early [[redox|reducing]] atmosphere into an oxidizing one, which [[Oxygen Catastrophe|dramatically changed]] the life forms on Earth and provoked an explosion of [[biodiversity]]. [[Chloroplast]]s in plants and eukaryotic [[algae]] have evolved from cyanobacteria. ==Forms== Cyanobacteria are found in almost every conceivable habitat, from oceans to fresh water to bare rock to soil. Most are found in fresh water, while others are marine, occur in damp soil, or even temporarily moistened rocks in [[desert]]s. A few are [[endosymbiont]]s in [[lichen]]s, plants, various [[protist]]s, or [[sea sponge|sponge]]s and provide energy for the [[Host (biology)|host]]. Some live in the fur of [[sloth]]s, providing a form of [[camouflage]] while they are safe. [[Image:CyanobacteriaColl1.jpg|thumb|right|250px|Colonies of ''[[Nostoc pruniforme]]''.]] Cyanobacteria include unicellular and [[colony (biology)|colonial]] species. Colonies may form [[filamentation|filaments]], sheets or even hollow balls. Some filamentous colonies show the ability to differentiate into several different [[cell (biology)|cell]] types: vegetative cells, the normal, photosynthetic cells that are formed under favorable growing conditions; akinetes, the climate-resistant spores that may form when environmental conditions become harsh; and thick-walled [[heterocysts]], which contain the enzyme nitrogenase, vital for [[nitrogen fixation]]. Heterocysts may also form under the appropriate environmental conditions (anoxic) wherever nitrogen is necessary. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas, which cannot be used by plants, into [[ammonia]] ({{nh3}}), [[nitrites]] ({{no2-}}) or [[nitrates]] ({{no3-}}), which can be absorbed by plants and converted to protein and nucleic acids. The [[rice]] paddies of [[Asia]], which produce about 75% of the world's rice<ref>[http://r0.unctad.org/infocomm/anglais/rice/market.htm United Nations Conference on Trade and Development]</ref>, could not do so were it not for healthy populations of nitrogen-fixing cyanobacteria in the rice paddy fertilizer too. Many cyanobacteria also form motile filaments, called [[hormogonium|hormogonia]], that travel away from the main biomass to bud and form new colonies elsewhere. 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. In order to break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium. Each individual cell of a cyanobacterium typically has a thick, gelatinous [[cell wall]]. They differ from other [[gram-negative]] bacteria in that the [[quorum sensing]] molecules autoinducer-2<ref> {{cite journal |author=J. Sun, ''et al.'' |year=2004 |title=Is autoinducer-2 a universal signal for interspecies communication? A comparative genomic and phylogenetic analysis of the synthesis and signal transduction pathways |journal=BMC Evol. Biol. |volume=4 |pages=36 |doi=10.1186/1471-2148-4-36 }}</ref> and acyl-homoserine lactones<ref> {{cite journal |author=E. Dittmann, ''et al.'' |year=2001 |title=Altered expression of two light-dependent genes in a microcystin-lacking mutant of ''Microcystis aeruginosa'' PCC7806 |journal=Microbiology |volume=147 |pages=3113–3119 }}</ref> are absent. They lack [[flagellum|flagella]], but hormogonia and some unicellular species may move about by [[bacterial gliding|gliding]] along surfaces. In water columns some cyanobacteria float by forming gas vesicles, like in [[archaea]]. ==Photosynthesis== Cyanobacteria have an elaborate and highly organized system of internal membranes which function in [[photosynthesis]]. Photosynthesis in cyanobacteria generally uses water as an [[redox|electron donor]] and produces [[oxygen]] as a by-product, though some may also use [[hydrogen sulfide]] as occurs among other photosynthetic bacteria. [[Carbon dioxide]] is reduced to form [[carbohydrate]]s via the [[Calvin cycle]]. In most forms the photosynthetic machinery is embedded into folds of the cell membrane, called [[thylakoid]]s. The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria. Due to their ability to fix nitrogen in [[aerobic]] conditions they are often found as [[symbiont]]s with a number of other groups of organisms such as fungi ([[lichen]]s), [[coral]]s, [[pteridophyte]]s (Azolla), [[angiosperm]]s (''[[Gunnera]]'') etc. Cyanobacteria are the only group of organisms that are able to reduce nitrogen and carbon in [[aerobic]] conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of [[photosystem]] (PS) II and I ([[Z-scheme]]). In [[anaerobic]] conditions, they are also able to use only PS I &mdash; cyclic photophosphorylation &mdash; with electron donors other than water ([[hydrogen sulfide]], thiosulphate, or even molecular hydrogen) just like [[purple bacteria|purple photosynthetic bacteria]]. Furthermore, they share an [[archaea]]l property, the ability to reduce elemental sulfur by anaerobic respiration in the dark. Their photosynthetic electron transport shares the same compartment as the components of respiratory electron transport. Actually, their plasma membrane contains only components of the respiratory chain, while the [[thylakoid]] membrane hosts both respiratory and photosynthetic electron transport. Attached to thylakoid membrane, [[phycobilisome]]s act as light harvesting antennae for the photosystems . The phycobilisome components ([[phycobiliprotein]]s) are responsible for the blue-green pigmentation of most cyanobacteria. The variations to this theme is mainly due to [[carotenoid]]s and [[phycoerythrin]]s which give the cells the red-brownish coloration. In some cyanobacteria, the color of light influences the composition of phycobilisomes. In green light, the cells accumulate more phycoerythrin, whereas in red light they produce more phycocyanin. Thus the bacteria appear green in red light and red in green light. This process is known as complementary chromatic adaptation and is a way for the cells to maximize the use of available light for photosynthesis. A few genera, however, lack phycobilisomes and have chlorophyll ''b'' instead (''[[Prochloron]]'', ''[[Prochlorococcus]]'', ''[[Prochlorothrix]]''). These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria. For this reason they are now considered as part of cyanobacterial group. ==Relationship to chloroplasts== <div class="thumb tright" style="border: 1px solid #CCCCCC; margin:0.5em;"> {|border="0" cellpadding="2" cellspacing="0" |{{clade| style="font-size:75%;line-height:75%" |1={{clade | 2={{clade | 2={{clade | 2=all other cyanobacteria | 1=[[plastid]]s }} | 1={{clade | 1=''[[Prochlorococcus]]'' | 2=''[[Synechococcus]]'' }} }} | 1=''[[Gloeobacter]]'' }} }} |} <div style="border: none;"><div class="thumbcaption"><small>Cladogram showing plastids (chloroplasts <br>and similar) and basal cyanobacteria.<ref>{{cite book | title=The Cyanobacteria: Molecular Biology, Genomics and Evolution | url=http://books.google.com/books?hl=sv&lr=&id=xgMahO1BXrQC&oi=fnd&pg=PA1&ots=m58kg-1Qno&sig=mt9OxD-__GmdITpqr11TtyLfzkM#PPA3,M1| author=Enrique Flores AH| date=2008| pages=3| publisher=Horizon| isbn=1904455158}}</ref></small></div></div></div> [[Chloroplast]]s found in [[Eukaryota|eukaryote]]s (algae and plants) likely evolved from an endosymbiotic relation with cyanobacteria. This [[endosymbiotic theory]] is supported by various structural and [[genetic]] similarities. Primary chloroplasts are found among the [[plant|green plants]], where they contain chlorophyll ''b'', and among the [[red alga]]e and [[glaucophyte]]s, where they contain phycobilins. It now appears that these chloroplasts probably had a single origin, in an ancestor of the [[clade]] called [[Primoplantae]]. Other algae likely took their chloroplasts from these forms by secondary endosymbiosis or ingestion. It was once thought that the [[Mitochondrion|mitochondria]] in eukaryotes also developed from an endosymbiotic relationship with cyanobacteria; however, it is now suspected that this evolutionary event occurred when aerobic bacteria were engulfed by anaerobic host cells. Mitochondria are believed to have originated not from cyanobacteria but from an ancestor of ''[[Rickettsia]]''. ==Cyanobacteria and Earth history== The biochemical capacity to use water as the source for electrons in [[photosynthesis]] evolved once, in a common ancestor of extant cyanobacteria. The geologic record indicates that this transforming event took place early in our planet's history, at least 2450-2320 million years ago (Ma), and possibly much earlier. Geobiological interpretation of [[Archean]] (>2500 Ma) sedimentary rocks remains a challenge; available evidence indicates that life existed 3500 Ma, but the question of when oxygenic [[photosynthesis]] evolved continues to engender debate and research. A clear paleontological window on cyanobacterial [[evolution]] opened about 2000 Ma, revealing an already diverse [[biota]] of blue-greens. Cyanobacteria remained principal primary producers throughout the [[Proterozoic Eon]] (2500-543 Ma), in part because the redox structure of the oceans favored photautotrophs capable of [[nitrogen fixation]]. Green [[algae]] joined blue-greens as major primary producers on continental shelves near the end of the [[Proterozoic]], but only with the [[Mesozoic]] (251-65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic [[gyre]]s, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.<ref name=Herrero>{{cite book | author = Herrero A and Flores E (editor). | title = The Cyanobacteria: Molecular Biology, Genomics and Evolution | edition = 1st ed. | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/cyan | id = [http://www.horizonpress.com/cyan ISBN 978-1-904455-15-8 ]}}</ref> ==Cyanobacterial evolution from comparative genomics== Recent high-throughput [[sequencing]] has provided DNA sequences at an unprecedented rate, posing considerable analytical challenges, but also offering insight into the genetic mechanisms of adaptation. Here we present a comparative genomics-based approach towards understanding the [[evolution]] of these mechanisms in cyanobacteria. Historically, systematic methods of defining morphological traits in cyanobacteria have posed a major barrier in reconstructing their true evolutionary history. The advent of [[protein]], then [[DNA]], sequencing - most notably the use of 16S [[rRNA]] as a molecular marker - helped circumvent this barrier and now forms the basis of our understanding of the history of life on Earth. However, these tools have proved insufficient for resolving relationships between closely related cyanobacterial species. The 24 cyanobacteria whose genomes have been compared occupy a wide variety of environmental niches and play major roles in global [[carbon]] and [[nitrogen]] cycles. By integrating phylogenetic data inferred for hundreds to nearly 1000 protein coding genes common to all or most cyanobacteria, we are able to reconstruct an evolutionary history of the entire [[phylum]], establishing a framework for resolving how their metabolic and phenotypic diversity came about.<ref name=Herrero>{{cite book | author = Herrero A and Flores E (editor). | title = The Cyanobacteria: Molecular Biology, Genomics and Evolution | edition = 1st ed. | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/cyan | id = [http://www.horizonpress.com/cyan ISBN 978-1-904455-15-8 ]}}</ref> ==Classification== The cyanobacteria were traditionally classified by morphology into five sections, referred to by the numerals I-V. The first three - [[Chroococcales]], [[Pleurocapsales]], and [[Oscillatoriales]] - are not supported by phylogenetic studies. However, the latter two - [[Nostocales]] and [[Stigonematales]] - are monophyletic, and make up the heterocystous cyanobacteria. The members of Chroococales are unicellular and usually aggregated in colonies. The classic taxonomic criterion has been the cell morphology and the plane of cell division. In Pleurocapsales, the cells have the ability to form internal spores (baeocytes). The rest of the sections include filamentous species. In Oscillatorialles, the cells are uniseriately arranged and do not form specialized cells (akinets and heterocysts). In Nostocalles and Stigonematalles the cells have the ability to develop heterocysts in certain conditions. Stigonematales, unlike Nostocalles include species with truly branched trichome. Most taxa included in the phylum or division Cyanobacteria have not yet been validly published under the [[International Code of Nomenclature of Bacteria|Bacteriological Code]]. Except: * The classes [[Chroobacteria]], [[Hormogoneae]] and [[Gloeobacteria]] * The orders [[Chroococcales]], [[Gloeobacterales]], [[Nostocales]], [[Oscillatoriales]], [[Pleurocapsales]] and [[Stigonematales]] * The families [[Prochloraceae]] and [[Prochlorotrichaceae]] * The genera [[Halospirulina]], [[Planktothricoides]], [[Prochlorococcus]], [[Prochloron]], [[Prochlorothrix]]. ==Biotechnology and applications== Certain cyanobacteria produce [[cyanotoxin]]s like [[anatoxin-a]], [[anatoxin-as]], [[aplysiatoxin]], [[cylindrospermopsin]], [[domoic acid]], [[microcystin LR]], [[nodularin R]] (from ''[[Nodularia]]''), or [[saxitoxin]]. Sometimes a mass-[[reproduction]] of cyanobacteria results in [[algal bloom]]s. The unicellular cyanobacterium ''[[Synechocystis]]'' sp. PCC6803 was the third prokaryote and first photosynthetic organism whose [[genome]] was completely [[DNA sequencing|sequenced]].<ref> {{cite journal |author=T. Kaneko, ''et al.'' |year=1996 |title= Kaneko, T. et al. (1996) Sequence analysis of the genome of the unicellular cyanobacterium ''Synechocystis'' sp. strain PCC6803. II. Sequence determination of the entire genome and assignment of potential protein-coding regions |journal=DNA Res. |volume=3 |pages=109–136 |doi= 10.1093/dnares/3.3.109 |pmid= 8905231 }}</ref> It continues to be an important model organism.<ref>{{cite journal |author=Tabei Y, Okada K, Tsuzuki M |title=Sll1330 controls the expression of glycolytic genes in Synechocystis sp. PCC 6803 |journal=Biochem. Biophys. Res. Commun. |volume=355 |issue=4 |pages=1045–50 |year=2007 |pmid=17331473 |doi=10.1016/j.bbrc.2007.02.065}}</ref> The smallest genomes have been found in ''[[Prochlorococcus]]'' spp. (1.7 Mb)<ref> {{cite journal |author=G. Rocap, ''et al.'' |year=2003 |title=Genome divergence in two ''Prochlorococcus'' ecotypes reflects oceanic niche differentiation |journal=[[Nature (journal)|Nature]] |volume=424 |pages=1042–1047 |doi=10.1038/nature01947 }}</ref><ref> {{cite journal |author=A. Dufresne, ''et al.'' |year=2003 |title=Genome sequence of the cyanobacterium ''Prochlorococcus marinus'' SS120, a nearly minimal oxyphototrophic genome. |journal=[[Proc. Natl Acad. Sci. USA]] |volume=100 |pages=10020–10025 |doi=10.1073/pnas.1733211100 |pmid=12917486 }}</ref> and the largest in ''[[Nostoc]] punctiforme'' (9 Mb)<ref> {{cite journal |author=J.C. Meeks, ''et al.'' |year=2001 |title=An overview of the genome of ''Nostoc punctiforme'', a multicellular, symbiotic cyanobacterium |journal=Photosynth. Res. |volume=70 |pages=85–106 A number of important advances have occurred in cyanobacterial biotechnology in the recent years. World wide attention is drawn towards cyanobacteria for their possible use in mariculture, food, feed, fuel, fertilizer, colourant, production of various secondary metabolites including vitamins, toxins, enzymes, pharmaceuticals, pharmacological probes and pollution abatement. Only a few cyanobacterial strains (including Spirulina) have been well-characterized or exploited commercially (Thajuddin and Subramanian. Cyanobacterial biodiversity and potential applications in biotechnology. CURRENT SCIENCE, VOL. 89, NO. 1, 10 JULY 2005) |doi=10.1023/A:1013840025518 }}</ref>. Those of ''[[Calothrix]]'' spp. are estimated at 12-15 Mb,<ref> {{cite journal |author=M. Herdman, ''et al.'' |year=1979 |title=Genome size of cyanobacteria |journal=J. Gen. Microbiol. |volume=111 |pages=73–85 }}</ref> as large as [[yeast]]. At least one secondary metabolite, cyanovirin, has shown to possess anti-[[HIV]] activity. See [[hypolith]] for an example of cyanobacteria living in extreme conditions. Some cyanobacteria are sold as food, notably ''Aphanizomenon flos-aquae'' and ''Arthrospira platensis'' ([[Spirulina (dietary supplement)|Spirulina]]). It has been suggested that they could be a much more substantial part of human food supplies, as a kind of [[superfood]]. Along with [[algae]], some hydrogen producing cyanobacteria are being considered as an [[alternative energy]] source, notably at [[Oregon State University]], in research supported by the U.S. Department of Energy, [[Princeton University]], [[Colorado School of Mines]], [[Ohio University]] as well as at [[Uppsala University]], Sweden. ==Health risks== Some species of cyanobacteria produce [[neurotoxins]], [[hepatotoxins]], [[cytotoxins]], and [[endotoxins]], making them dangerous to animals and humans. Several cases of human poisoning have been documented but a lack of knowledge prevents an accurate assessment of the risks.<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8830224&dopt=Abstract Cyanobacteria, their toxins and health risks]</ref><ref>[http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/cyanobacter_e.html Blue-Green Algae (Cyanobacteria) and their Toxins]</ref> ==See also== * [[Oxygen Catastrophe]] * [[Archean]] * [[Proterozoic]] ==References== {{reflist}} * Gillian Cribbs (1997) ''Nature's Superfood, the Blue-Green Algae Revolution''. Newleaf. ISBN 0-7522-0569-2 * [[Marshall Savage]], (1992, 1994) [[The Millennial Project: Colonizing the Galaxy in Eight Easy Steps]]. Little, Brown. ISBN 0-316-77163-5 * Dyer, Betsey D. A Field Guide to Bacteria. Ithaca: Comstock Publishing Associates, 2003. * Fogg, G.E., Stewart, W.D.P., Fay, P.and Walsby, A.E. 1973. ''The Blue-green Algae.'' Academic Press, London and New York. ISBN 0-12-261650-2 * [http://www.ucmp.berkeley.edu/bacteria/cyanointro.html "Architects of the earth's atmosphere."] Introduction to the Cyanobacteria. [[University of California, Berkeley]]. 03 Feb. 2006. * Whitton, B.A. Phylum Cyanophyta (Cyanobacteria). in ''The Freshwater Algal Flora of the British Isles.'' [[Cambridge University Press]], Cambridge ISBN 0 521 77051 3 ==External links== {{commonscat|Cyanobacteria}} * [http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT311/Cyanobacteria/Cyanobacteria.htm Overview of cyanobacteria] * [http://www-cyanosite.bio.purdue.edu Webserver for Cyanobacteria Research] * [http://www.horizonpress.com/gateway/cyanobacteria.html Cyanobacteria] * [http://space.newscientist.com/article/dn13465-hardy-earth-bacteria-can-grow-in-lunar-soil.html?feedId=online-news_rss20 Hardy Earth bacteria can grow in lunar soil] - resilient cyanobacteria could help future lunar colonists to extract lunar resources, ''New Scientist'', 14 March 2008 [[Category:Phototrophic bacteria]] [[Category:Cyanobacteria|*]] [[Category:Photosynthesis]] [[bs:Modrozelene alge]] [[bg:Синьо-зелена плесен]] [[ca:Cianobacteri]] [[cs:Sinice]] [[da:Cyanobakterie]] [[de:Cyanobakterien]] [[et:Sinivetikad]] [[el:Κυανοβακτήρια]] [[es:Cyanobacteria]] [[eo:Cianobakterio]] [[fr:Cyanobacteria]] [[gl:Cyanobacteria]] [[ko:남조류]] [[hr:Modrozelene alge]] [[id:Cyanobacteria]] [[it:Cyanobacteria]] [[he:כחוליות]] [[ka:ლურჯ-მწვანე წყალმცენარეები]] [[lt:Melsvabakterės]] [[hu:Cianobaktériumok]] [[nl:Blauwalgen]] [[ja:藍藻]] [[no:Cyanobakterier]] [[nn:Cyanobakterie]] [[pl:Sinice]] [[pt:Cyanobacteria]] [[qu:Anqas añaki]] [[ru:Цианобактерии]] [[simple:Cyanobacteria]] [[sk:Sinice]] [[sr:Модрозелене бактерије]] [[fi:Syanobakteerit]] [[sv:Cyanobakterier]] [[th:สาหร่ายสีเขียวแกมน้ำเงิน]] [[vi:Vi khuẩn lam]] [[tr:Siyanobakteri]] [[uk:Ціанобактерії]] [[zh:藍菌]]