{{short description|Virus that infects cyanobacteria}} {{cs1 config|name-list-style=vanc}} [[Image:Cyanophages.png|thumb|300px|right|Electron micrograph of negative-stained Prochlorococcus myoviruses]] '''Cyanophages''' are viruses that infect cyanobacteria, also known as Cyanophyta or blue-green algae. Cyanobacteria are a phylum of bacteria that obtain their energy through the process of photosynthesis.<ref name=":8" /><ref>{{Cite book|title=The Ecology of Cyanobacteria: Their Diversity in Time and Space|last1=Whitton|first1=Brian A.|last2=Potts|first2=Malcolm|publisher=Kluwer Academic|year=2000|isbn=978-0-7923-4735-4|location=Boston|pages=563–589}}</ref> Although cyanobacteria metabolize photoautotrophically like eukaryotic plants, they have prokaryotic cell structure. Cyanophages can be found in both freshwater and marine environments.<ref name=":2" /> Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins.<ref name=":20">{{Cite journal|last1=Suttle|first1=Curtis A.|last2=Chan|first2=Amy M.|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 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 12% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.<ref name="Gochev ">{{Cite journal|last1=Gochev |first1=Shopen|year=2025|title=Cold Surface Waters of the Sub-Antarctic Pacific Ocean Support High Cyanophage Abundances and Infection Levels|journal=Environ Microbiol.|volume=27|issue=1|article-number=e70031 |doi=10.1111/1462-2920.70031 |pmid=39797436 |pmc=11724200 }}</ref>

The first described cyanophage LPP-1, was reported by Safferman and Morris in 1963.<ref name=Sarma /> Historically, cyanophages were classified by morphotype within the bacteriophage families ''Myoviridae'' (e.g. AS-1, N-1), ''Podoviridae'' (e.g. LPP-1) and ''Siphoviridae'' (e.g. S-1).<ref name=Sarma>Sarma TA. 'Cyanophages' in ''Handbook of Cyanobacteria'' (CRC Press; 2012) ({{ISBN|1466559411}})</ref>

==Nomenclature== The following three families of cyanophages have been recognized by the International Committee on Taxonomy of Viruses (ICTV): Myoviridae, Siphoviridae and Podoviridae; all contain double-stranded DNA.<ref>{{Cite book|title=Virus Taxonomy Classification and Nomenclature of Viruses: Ninth Report of the International Committee on Taxonomy of Viruses|last1=King|first1=A.M.Q.|last2=Lefkowitz|first2=E.|last3=Adams|first3=M.J.|last4=Carstens|first4=E.B.|publisher=Elsevier|year=2012|isbn=978-0-12-384684-6}}</ref> Initially, cyanophages were named after their hosts. However, the ability of cyanophages to infect multiple hosts and lack of a universal naming system can cause difficulties with their taxonomic classification.<ref name=":17">{{Cite journal|last1=Safferman|first1=R.S.|last2=Cannon|first2=R.E.|last3=Desjardins|first3=P.R.|last4=Gromov|first4=B.V.|author5-link=Robert Haselkorn|last5=Haselkorn|first5=R.|last6=Sherman|first6=L.A.|last7=Shilo|first7=M.|title=Classification and Nomenclature of Viruses of Cyanobacteria|journal=Intervirology|volume=19|issue=2|pages=61–66|doi=10.1159/000149339|pmid=6408019|year=1983|doi-access=free}}</ref> Many other classification systems used serological, morphological, or physiological properties.<ref>{{Cite book|title=Molecular Bases of Virus Evolution|last=Gibbs|first=Adrian J|publisher=Cambridge University Press|year=2005|isbn=978-0-521-02289-7}}</ref><ref>{{Cite journal|last=Stanier|first=R.Y.|year=1971|title=Purification and properties of unicellular blue-green algae (order Chroocococcales)|pmc=378380|journal=Bacteriological Reviews|volume=35|issue=2|pages=171–205|pmid=4998365|doi=10.1128/MMBR.35.2.171-205.1971}}</ref> Currently, the suggested procedure of naming strains is as follows: Cyanophage Xx-YYZaa, where Xx is the first two letters of the genus and species names of the host that the type specimen phage is found in, YY is the origin of the specimen, Z is the virus family, and aa is the reference number of the virus.<ref name=":2" />

==Morphology== Like all other tailed bacteriophages cyanophages have a tail and a protein capsid surrounding genetic material. The double-stranded DNA is approximately 45 kilo-base-pairs long and in some cyanophages encodes photosynthetic genes, an integrase, or genes involved with phosphate metabolism (phosphate-inducible).<ref name=":19">{{Cite journal|last1=Sullivan|first1=Matthew B.|last2=Coleman|first2=Maureen L.|last3=Weigele|first3=Peter|last4=Rohwer|first4=Forest|last5=Chisholm|first5=Sallie W.|date=2005-04-19|title=Three Prochlorococcus Cyanophage Genomes: Signature Features and Ecological Interpretations|journal=PLOS Biology|volume=3|issue=5|page=e144|doi=10.1371/journal.pbio.0030144|issn=1545-7885|pmc=1079782|pmid=15828858 |doi-access=free }}</ref> The tail binds the virus to the host cell and transfers viral DNA to the host cell upon infection. Based on morphological characteristics, cyanophages are placed into the families Myoviridae, Podoviridaeand Siphoviridae, and although not formally recognized by the International Committee on Taxonomy of Viruses, historically cyanophages have been further classified into as a Cyanomyovirus, Cyanopodovirus or Cyanostylovirus based on which of the three families in which they are grouped.<ref name=":17" />

=== Cyanomyovirus === The type species for Cyanomyovirus of the family ''Myoviridae'' is Cyanophage AS-1, which was isolated from a waste stabilization pond,<ref name=":0">{{Cite journal|last1=Safferman|first1=R.S.|last2=Diener|first2=T.O.|last3=Desjardins|first3=P.R.|last4=Morris|first4=M.E.|title=Isolation and characterization of AS-1, a phycovirus infecting the blue-green algae, ''Anacystis nidulans'' and ''Synechococcus cedrorum''|journal=Virology|language=en|volume=47|issue=1|pages=105–113|doi=10.1016/0042-6822(72)90243-7|pmid=4110125|year=1972}}</ref> and was also the first genus recognized.<ref name=":18">{{Cite journal|last1=Safferman|first1=Robert S.|last2=Morris|first2=Mary-Ellen|year=1964|pmc=277376|journal=J. Bacteriol.|volume=88|issue=3|pages=771–775|pmid=14208517|title=Growth Characteristics of the Blue-Green Algal Virus LPP-1|doi=10.1128/JB.88.3.771-775.1964 |bibcode=1964JBact..88..771S }}</ref> The tails have been observed as either contractile or noncontractile with lengths of 20 to 244&nbsp;nm, widths of 15 to 23&nbsp;nm, and a shrinking range of 93&nbsp;nm.<ref name=":1">{{Cite journal|last1=Padan|first1=E.|last2=Shilo|first2=M.|year=1973|title=Cyanophages- viruses attacking blue-green algae.|pmc=413822|journal=Bacteriological Reviews|volume=37 |issue=3|pages=343–370|pmid=4202147|doi=10.1128/MMBR.37.3.343-370.1973}}</ref><ref name=":2">{{Cite book|title=The Ecology of Cyanobacteria|last=Suttle|first=Curtis A.|date=2000-01-01|publisher=Springer Netherlands|isbn=978-0-7923-4735-4|editor-last=Whitton|editor-first=Brian A.|pages=563–589|language=en|doi=10.1007/0-306-46855-7_20|editor-last2=Potts|editor-first2=Malcolm|chapter = Cyanophages and Their Role in the Ecology of Cyanobacteria}}</ref> Cyanophages generally have isometric hexagonal heads with diameters ranging from 55 to 90&nbsp;nm.<ref name=":1" /><ref name=":2" /> There is large morphological variation in this group, which suggests that they infect a variety of host species.<ref name=":3">{{Cite journal|last=Gromov|first=B.V.|title=Cyanophages|journal=Annales de l'Institut Pasteur / Microbiologie|language=en|volume=134|issue=1|pages=43–59|doi=10.1016/s0769-2609(83)80096-9|pmid=6416127|year=1983}}</ref> At the point of attachment between the long tail and the head there is a base plate where short pins are attached, a contractile sheath, and an internal core, similar to other bacteriophages in the Myoviridae.<ref name=":0" />

=== Cyanopodovirus === Cyanopodovirus, within the ''Podoviridae'', are present in both fresh and marine water.<ref>{{Cite journal|last1=Hu|first1=Nien-Tai|last2=Thiel|first2=Teresa|last3=Giddings|first3=Thomas H.|last4=Wolk|first4=C.Peter|title=New Anabaena and Nostoc cyanophages from sewage settling ponds|journal=Virology|language=en|volume=114|issue=1|pages=236–246|doi=10.1016/0042-6822(81)90269-5|pmid=6269286|year=1981 }}</ref> The type specimen of cyanopodovirus is Cyanophage LPP-1, which infects ''Lyngbya'', ''Plectonema'' and ''Phormidium''.<ref>{{Cite journal|last1=Schneider|first1=I. R.|last2=Diener|first2=T. O.|last3=Safferman|first3=Robert S.|date=1964-05-29|title=Blue-Green Algal Virus LPP-1: Purification and Partial Characterization|journal=Science|language=en|volume=144|issue=3622|pages=1127–1130|doi=10.1126/science.144.3622.1127|issn=0036-8075|pmid=14148431|bibcode=1964Sci...144.1127S|s2cid=45125402}}</ref> Their capsids are polyhedrons that appear hexagonal in 2-D.<ref name=":1" /> The tails are hollow with sixfold radial symmetry made of rings of six subunits with unknown orientation.<ref name=":1" /> Similar to cyanomyoviruses, they can be found in waste-stabilization ponds and have isometric capsids of similar size but shorter tails.<ref name=":2" />

=== Cyanostylovirus === Cyanostylovirus belong to the family ''Siphoviridae'', where the type species is Cyanophage S-1, which is known to infect ''Synechococcus''.<ref name=":2" /> Cyanostyloviridae have smaller (50&nbsp;nm in diameter) isometric capsids than the previous genera but longer tails (140&nbsp;nm).<ref name=":4">{{Cite journal|last1=Adolph|first1=Kenneth W.|last2=Haselkorn|first2=Robert|title=Isolation and characterization of a virus infecting a blue-green alga of the genus ''Synechococcus''|journal=Virology|language=en|volume=54|issue=1|pages=230–236|doi=10.1016/0042-6822(73)90132-3|pmid=4197413|year=1973}}</ref> Other genera in this family have tails that range from 200 to 300&nbsp;nm in length.<ref name=":3" />

==Host== [[File:Anabaena circinalis.jpg|thumb|''Anabaena circinalis'' filament]] The host range of cyanophages is very complex and is thought to play an important role in controlling cyanobacterial populations.<ref name=":8">{{Cite journal|last1=Xia|first1=Han|last2=Li|first2=Tianxian|last3=Deng|first3=Fei|last4=Hu|first4=Zhihong|date=2013-10-01|title=Freshwater cyanophages|journal=Virologica Sinica|language=en|volume=28|issue=5|pages=253–259|doi=10.1007/s12250-013-3370-1|pmid=24132756|pmc=8208336|issn=1674-0769}}</ref> Freshwater cyanophages have been reported to infect hosts in more than one genus although this may also reflect problems in the taxonomic classification of their hosts. Nonetheless, they have been classified into three major groups based on the taxonomy of their host organism.<ref name=":8" /><ref name=":2" />

=== LPP group === The first group is LPP, which belongs to the cyanopodoviruses.<ref name=":8" /> This group of viruses includes the original cyanophage isolate that infected "blue-green algae".<ref name=":18" /><ref name=":2" /> Cyanophages in this group are easy to isolate from the environment.<ref name=":2" /> They carry short non-contractile tails and cause lysis of several species within three genera of cyanobacteria: ''Lyngbya'', ''Plectonema'' and ''Phormidium''.<ref name=":2" /> Thus, the name LPP was derived from the three genera of hosts that they infect.<ref name=":18" /> LPP-1 and LPP-2 are two major types of LPP cyanhophages.<ref name=":15">{{Cite journal|last1=JOHNSON|first1=DAVID W.|last2=POTTS|first2=MALCOLM|year=1985|title=Host Range of LPP Cyanophages|journal=International Journal of Systematic Bacteriology|volume=35|pages=76–78|doi=10.1099/00207713-35-1-76|doi-access=free}}</ref> This group of cyanophages has the same host same range; however, their serum and other body fluids are not the same.<ref name=":15" />

=== AS and SM group === The AS and SM groups represent the third group of cyanophages classified based on host range.<ref name=":8" /> This group of viruses is said to be the "new blue-green algae" and infects unicellular forms of cyanobacteria.<ref name=":2" /><ref>{{Cite journal|last1=SAFFERMAN|first1=R.S|last2=Schneider|first2=I.R.|last3=Steere|first3=R.L.|last4=MORRIS|first4=M.E.|last5=DIENER|first5=T.O|year=1969|title=Phycovirus SM-1: A virus infecting unicellular blue-green algae|journal=Virology|volume=37|issue=3|pages=386–397|doi=10.1016/0042-6822(69)90222-0|pmid=5777559}}</ref><ref name=":0" /> The myovirus AS-1 infects ''Anacystis nidulans'',<ref name="pmid4209657">{{cite journal |vauthors=Orkwiszewski KG, Kaney AR |s2cid=5635245 |title=Genetic transformation of the blue-green bacterium, Anacystis nidulans |journal=Arch Mikrobiol |volume=98 |issue=1 |pages=31–37 |date=June 1974 |pmid=4209657 |doi= 10.1007/BF00425265|bibcode=1974ArMic..98...31O }}</ref> ''Synechococcus cedrorum'', ''Synechococcus elongatus'' and ''Microcystis aeruginosa''.<ref name=":2" /> Similarly, the unicellular blue-green algae ''Synechococcus elongatus'' and ''Microcystis aeruginosa'' are infected by the podovirus SM-1.<ref name=":2" /><ref name=":16">{{Cite journal|last1=Fox|first1=John A.|last2=Booth|first2=S.J.|last3=Martin|first3=E.L.|year=1976|title=Cyanophage SM-2: A new blue-green algal virus|journal=Virology|volume=73|issue=2|pages=557–560|doi=10.1016/0042-6822(76)90420-7|pmid=8869}}</ref> There is a new SM-group of virus, known as SM-2, which also lyses ''Microcystis aeruginosa''<ref name=":16" />''.''

=== A, AN, N and NP group === Cyanophages classified in the groups A, AN, N and NP represent a second group of cyanophages classified based on host range.<ref name=":4" /><ref name=":8" /><ref>{{Cite journal|last=MURADOV|first=MM|year=1990|title=COMPARATIVE-STUDY OF NP-1T CYANOPHAGES, WHICH LYSOGENIZE NITROGEN-FIXING BACTERIA OF THE GENERA NOSTOC AND PLECTONEMA|journal=Microbiology|volume=59|issue=5|pages=558–563}}</ref><ref>{{Cite journal|last=Kozayakov|first=SYa|year=1977|title=Cyanophages of the series A(L) specific for the blue-green alga ''Anabaena variabilis''. In|journal=Experimental Algology|pages=151–171}}</ref> They play an important role in infecting and causing lysis of members of the genera ''Nostoc'', ''Anabaena'' and ''Plectonema''.<ref name=":8" /> The A-group of the virus causes lysis and infects ''Anabaena'' species.<ref name=":2" /> Similarly, the host range of the AN group includes both ''Anabaena'' and ''Nostoc'' species; whereas, the N group of viruses infects ''Nostoc'' species only and includes Cyanophage N-1.<ref name=":2" /> Cyanophage N-1 is remarkable in that it encodes a functional CRISPR array that may provide immunity to the host to infection by competing cyanophages.<ref name=Chenard>{{citation|vauthors=Chénard C, Wirth JF, Suttle CA |title=Viruses Infecting a freshwater filamentous cyanobacterium (''Nostoc'' sp.) encode a functional CRISPR array and a proteobacterial DNA polymerase B|journal=mBio|volume=7|issue=3|article-number=e00667-16|year=2016|doi=10.1128/mBio.00667-16 |doi-access=free |pmid=27302758|pmc=4916379}}</ref> Lastly, cyanobacterial isolates of ''Nostoc'' and ''Plectonema'' species are infected by the NP group of viruses.<ref name=":2" /> These cyanobacterial isolates closely relate to the taxonomic group of ''Nostoc''.<ref name=":2" /> They all have a broad host range and mutations are noticeable in these groups of viruses.<ref name=":2" />

==Replication== Cyanophage replication has two dominant cycles: the lytic cycle and the lysogenic cycle. Viral nucleic-acid replication and immediate synthesis of virus-encoded protein is considered to be the lytic cycle. Phages are considered lytic if they only have the capacity to enter the lytic cycle; whereas, temperate phage can either enter the lytic cycle or become stably integrated with the host genome and enter the lysogenic cycle.<ref name=":9">{{Cite journal|last1=Jassim|first1=Sabah A. A.|last2=Limoges|first2=Richard G.|date=2013-10-01|title=Impact of external forces on cyanophage–host interactions in aquatic ecosystems|journal=World Journal of Microbiology and Biotechnology|language=en|volume=29|issue=10|pages=1751–1762|doi=10.1007/s11274-013-1358-5|pmid=23619821|bibcode=2013WJMB...29.1751J |s2cid=24177191|issn=0959-3993}}</ref> To meet the metabolic demand of replication, viruses recruit a multitude of strategies to sequester nutrients from their host. One such technique is to starve their host cell. This is done by inhibiting the host cells CO<sub>2</sub> fixation, which enables the cyanophage to recruit photosynthetically formed redox and ATP from the host cell to meet their nucleotide and metabolic response.<ref name=":10">{{Cite journal|last=Kaplan|first=Aaron|year=2016|title=Cyanophages: Starving the Host to Recruit Resources|doi=10.1016/j.cub.2016.04.030|pmid=27326715|journal=Cell|volume=26|issue=12|pages=R511–R513|doi-access=free|bibcode=2016CBio...26.R511K }}</ref> Many cyanophages contain genes known as viral-encoded auxiliary metabolic genes (AMGs), which encode critical, rate-limiting steps of the host organism.<ref name=":10" /> AMGs encode genes for the pentose phosphate pathway, phosphate acquisition, sulfur metabolism, and DNA/RNA processing; these genes interfere with the metabolism of the host cell. Metagenomic analysis highly supports the notion that these genes promote viral replication through the degradation of host DNA and RNA, as well as a shift in host-cell metabolism to nucleotide biosynthesis.<ref name=":10" /> Cyanophages also use these genes to maintain host photosynthesis through the progression of the infection, shuttling the energy away from carbon fixation to anabolism, which the virus takes advantage of.<ref name=":11">{{Cite journal|last1=Frank|first1=Jeremy A.|last2=Lorimer|first2=Don|last3=Youle|first3=Merry|last4=Witte|first4=Pam|last5=Craig|first5=Tim|last6=Abendroth|first6=Jan|last7=Rohwer|first7=Forest|last8=Edwards|first8=Robert A.|last9=Segall|first9=Anca M.|date=2013-06-01|title=Structure and function of a cyanophage-encoded peptide deformylase|journal=The ISME Journal|language=en|volume=7|issue=6|pages=1150–1160|doi=10.1038/ismej.2013.4|issn=1751-7362|pmc=3660681|pmid=23407310|bibcode=2013ISMEJ...7.1150F }}</ref> AMGs also code for proteins, which aid in the repair of the host photosystem, which is susceptible to photodegradation.<ref name=":11" /> One such example is the D1 proteins which replace the host cells D1 protein when it becomes damaged.<ref name=":11" /> The virus up-regulates photosynthesis, which leads to an increased rate of D1 protein degradation, the host cell alone can not efficiently replace these proteins so the cyanophage replaces them for the host cell, allowing it to continue providing energy for the cyanophage replication cycle.<ref name=":11" />

It is evident that cyanophage replication is heavily dependent on the diel cycle. The first step in the infectious cycle is for the cyanophage to make contact and bind to the cyanobacteria, this adsorption process is heavily dependent on light intensity.<ref name=":12">{{Cite journal|last1=Ni|first1=Tianchi|last2=Zeng|first2=Qinglu|date=2016-01-01|title=Diel Infection of Cyanobacteria by Cyanophages|journal=Frontiers in Marine Science|language=en|volume=2|page=123 |doi=10.3389/fmars.2015.00123|doi-access=free |bibcode=2016FrMaS...2..123N }}</ref> Field studies also show that the infection and replication of cyanophages is directly or indirectly synchronized with the light-dark cycle.<ref name=":12" />

=== Adherence === <!-- Deleted image removed: thumb|A bacteriophage adhering to its host --> Cyanophages like other bacteriophages 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=":14">{{Cite journal|last1=Fokine|first1=Andrei|last2=Rossmann|first2=Michael G.|date=2014-01-01|title=Molecular architecture of tailed double-stranded DNA phages |journal=Bacteriophage|volume=4|issue=1|article-number=e28281|doi=10.4161/bact.28281|pmid=24616838|pmc=3940491}}</ref> Cyanophages also have several surface proteins with Ig-like domains, which are used for adherence.<ref name=":14" />

=== Lytic cycle === Cyanophages can undergo both the lytic and lysogenic cycles depending on the viruses and their environment.<ref name=":McDaniel">{{Cite journal|last1=McDaniel|first1=Lauren |last2=Houchin |first2=Lee A. |last3=Williamson|first3=Shannon J. |last4=Paul |first4=John P. |date=2002 |title=Plankton blooms - Lysogeny in marine ''Synechococcus''|journal=Nature|language=en|volume=415|issue=6871 |page=496 |doi=10.1038/415496a|pmid=11823851 |bibcode=2002Natur.415..496M |s2cid=4418714 |doi-access=free }}</ref><ref name=":Ortmann">{{Cite journal|last1=Ortmann |first1=Alice C. |last2=Lawrence |first2=Janice E. |last3=Suttle |first3=Curtis A. |date=2002 |title=Lysogeny and lytic viral production during a bloom of the cyanobacterium ''Synechococcus'' spp. |journal=Microbial Ecology|language=en|volume=43|issue=2 |pages=225–231|doi=10.1007/s00248-001-1058-9|pmid=12023729 |bibcode=2002MicEc..43..225O |s2cid=27385452 }}</ref> In one study on cyanomyoviruses infecting marine ''Synechococcus'' sp., the lytic phase was shown to last approximately 17 hours with the average number of viruses produced for each cell that was lysed (burst size) ranging from 328 under high light to 151 under low light.<ref>{{Cite thesis|last=Brigden|first=Sean|date=2003|title=Dynamics of Cyanophage Replication |url=https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0091069|doi=10.14288/1.0091069|type=MSc, Botany|publisher=University of British Columbia}}</ref> There is evidence supporting the premise that there is a correlation between light intensity and burst size.<ref name=":12" /> Studies show that cyanophage replication is driven by energy from photosynthetic metabolism of the host cell.<ref name=":21">{{Cite journal|last1=Ni|first1=Tianchi|last2=Zeng|first2=Qinglu|date=2016-01-01|title=Diel Infection of Cyanobacteria by Cyanophages|journal=Frontiers in Marine Science|language=en|volume=2|doi=10.3389/fmars.2015.00123|issn=2296-7745|url=http://repository.ust.hk/ir/bitstream/1783.1-77187/1/2016NietalFrontiersMarineScience.pdf|doi-access=free |bibcode=2016FrMaS...2..123N }}</ref> Lysing of the host cell tends to occur after the completion of host DNA replication and immediately prior to cell division.<ref name=":21" /> This is likely due to the increased availability of intra-cellular resources for creating viral particles.<ref name=":21" />

==Ecological Significance== [[File:232757 web prochlorococcus marinus phage P-SSM2 Fd.jpg|thumb|When phage P-SSM2 Fd (''Myo&shy;viridae'', genus ''Salacisavirus'', pink) infects the ubiquitous ''Prochlorococcus marinus'' cyanobacteria, it produces a ferredoxin protein that hooks into the bacteria's existing electrical structure and alters its metabolism.<ref name="Campbell2020">Ian J. Campbell, Jose Luis Olmos Jr., Weijun Xu, Dimithree Kahanda, Joshua T. Atkinson, Othneil Noble Sparks, Mitchell D. Miller, George N. Phillips Jr., George N. Bennett, Jonathan J. Silberg: [https://www.jbc.org/content/early/2020/05/19/jbc.RA120.013501 ''Prochlorococcus'' phage ferredoxin: Structural characterization and electron transfer to cyanobacterial sulfite reductases] – Phage Fd characterization and host SIR interactions, in: J. Biol. Chem., ASBMB Publications, 19 May 2020, doi:10.1074/jbc.RA120.013501, [https://www.jbc.org/content/early/2020/05/19/jbc.RA120.013501.full.pdf PDF]. Along with: * Ocean virus hijacks carbon-storing bacteria, Source: Rice University :* [https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=300664&org=NSF&from=news National Science Foundation (NSF)], 29 May 2020 :* [https://www.eurekalert.org/pub_releases/2020-05/ru-ovh052220.php EurekAlert], 26 May 2020 :* [https://www.sciencedaily.com/releases/2020/05/200526091359.htm Ocean ScienceDaily], 26 May 2020 * [https://scitechdaily.com/beneath-the-oceans-surface-a-virus-is-hijacking-the-most-abundant-organism-on-earth/ Beneath the Ocean's Surface, a Virus Is Hijacking the Most Abundant Organism on Earth], on: SciTechDaily, 6 June 2020. Source: Rice University</ref>]] <!-- WP:NFCC violation: thumb|395x395px|Role of viruses and other marine microbes in carbon sequestration (biological pump) and macronutrient recycling (biogeochemical cycles). DOM = Dissolved Organic Matter; POM = Particulate Organic Matter. -->

=== Ecosystem === Certain cyanophages infect and burst ''Prochlorococcus'', the world's smallest and most abundant primary producers.<ref name=":22">{{Cite journal|last1=Partensky|first1=F.|last2=Hess|first2=W. R.|last3=Vaulot|first3=D.|date=1999-03-01|title=''Prochlorococcus'', a Marine Photosynthetic Prokaryote of Global Significance|journal=Microbiology and Molecular Biology Reviews|volume=63|issue=1|pages=106–127|issn=1092-2172|pmc=98958|pmid=10066832|doi=10.1128/MMBR.63.1.106-127.1999}}</ref><ref name=":19" /> Marine cyanophages of the family ''Myoviridae'' help regulate primary production mainly through infection of ''Synechococcus'' spp.<ref name=":2" /> The other two families, ''Podoviridae'' and ''Siphoviridae'', are usually found in freshwater ecosystems.<ref name=":2" /> In coastal oceans, abundance of viruses infecting ''Synechococcus'' spp. can reach >10<sup>6</sup> mL<sup>−1</sup> and 10<sup>5</sup> g<sup>−1</sup> in sediments.<ref name=":2" /> An estimated 3% of ''Synechococcus'' are removed daily by cyanophages.<ref name=":2" /> Cyanophages are widely distributed both throughout the water column and geographically.<ref name=":2" /><ref name=":22" /><ref name=":13">{{Cite journal|last1=Varin|first1=Thibault|last2=Lovejoy|first2=Connie|last3=Jungblut|first3=Anne D.|last4=Vincent|first4=Warwick F.|last5=Corbeila|first5=Jacques|s2cid=55550366|title=Metagenomic profiling of Arctic microbial mat communities as nutrient scavenging and recycling systems|journal=Limnology and Oceanography|volume=55|issue=5|pages=1901–1911|doi=10.4319/lo.2010.55.5.1901|year=2010|bibcode=2010LimOc..55.1901V|doi-access=free}}</ref> Cyanophage populations have been found to inhabit microbial mats in the Arctic through metagenomic analysis and hypersaline lagoons.<ref name=":13" /><ref name=":20" /> They can withstand temperatures ranging from 12 to 30&nbsp;°C and salinities of 18-70 ppt.<ref name=":20" /> The DNA of cyanophages is susceptible to UV degradation but can be restored in host cells through a process called "photoreactivation".<ref>{{Cite journal|last1=Cheng|first1=Kai|last2=Zhao|first2=Yijun|last3=Du|first3=Xiuli|last4=Zhang|first4=Yaran|last5=Lan|first5=Shubin|last6=Shi|first6=Zhengli|date=2007-06-20|title=Solar radiation-driven decay of cyanophage infectivity, and photoreactivation of the cyanophage by host cyanobacteria|journal=Aquatic Microbial Ecology|volume=48|issue=1|pages=13–18|doi=10.3354/ame048013|doi-access=free}}</ref> The viruses cannot move independently and must rely on currents, mixing, and host cells to transport them. Viruses cannot actively target their hosts and must wait to encounter them. The higher probability of collision may explain why cyanophages of the ''Myoviridae'' family primarily infect one of the most abundant cyanobacteria, ''Synechoccocus''.<ref name=":2" /> Evidence of seasonal co-variation between the phages and hosts, in addition to an increase in cyanophages above a threshold of 10<sup>3</sup> to 10<sup>4</sup> ''Synechococcus'' mL<sup>−1</sup>, may suggest a "kill-the-winner" dynamic.<ref name=":2" />

=== Biological and physical impact === Members of the genus ''Synechococcus'' contribute ~25% to photosynthetic primary productivity in the ocean, having significant bottom-up effect on higher trophic levels.<ref name=":5">{{Cite journal|last1=Wang|first1=Kui|last2=Wommack|first2=K. Eric|last3=Chen|first3=Feng|date=2011-11-01|title=Abundance and Distribution of ''Synechococcus'' spp. and Cyanophages in the Chesapeake Bay|journal=Applied and Environmental Microbiology|language=en|volume=77|issue=21|pages=7459–7468|doi=10.1128/AEM.00267-11|issn=0099-2240|pmc=3209163|pmid=21821760|bibcode=2011ApEnM..77.7459W }}</ref> The dissolved organic matter (DOM) released from viral lysis by cyanophages can be shunted into the microbial loop where it is recycled or rejected by heterotrophic bacteria to form recalcitrant matter that is eventually buried in sediment.<ref name=":5" /><ref name=":6">{{Cite journal|last=Weinbauer|first=Markus|year=2011|title=Virus-Mediated Redistribution and Partitioning of Carbon in the Global Oceans|journal=ResearchGate|pages=54–56}}</ref> This is an important step in atmospheric carbon sequestration, commonly referred to as the biological pump, and maintenance of other biogeochemical cycles.<ref name=":5" />

Cyanobacteria perform oxygenic photosynthesis which is thought to be the origin of atmospheric oxygen approximately 2.5Ga ago.<ref>{{Cite journal|last1=Schirrmeister|first1=Bettina E.|last2=Antonelli|first2=Alexandre|last3=Bagheri|first3=Homayoun C.|date=2011-01-01|title=The origin of multicellularity in cyanobacteria|journal=BMC Evolutionary Biology|volume=11|issue=1 |page=45|doi=10.1186/1471-2148-11-45|issn=1471-2148|pmc=3271361|pmid=21320320 |doi-access=free |bibcode=2011BMCEE..11...45S }}</ref> Population, and therefore, rate of oxygen evolution can be regulated by cyanophages. In certain species of cyanobacteria, such as ''Trichodesmium'' that perform nitrogen fixation, cyanophages are capable of increasing the supply rate of bioavailable organic nitrogen through lysis.<ref>{{Cite journal|last1=Bergman|first1=Birgitta|last2=Sandh|first2=Gustaf|last3=Lin|first3=Senjie|last4=Larsson|first4=John|last5=Carpenter|first5=Edward J.|date=2013-05-01|title=Trichodesmium– a widespread marine cyanobacterium with unusual nitrogen fixation properties|journal=FEMS Microbiology Reviews|volume=37|issue=3|pages=286–302|doi=10.1111/j.1574-6976.2012.00352.x|issn=0168-6445|pmc=3655545|pmid=22928644}}</ref><ref>{{Cite journal|last1=Kashyap|first1=A. K.|last2=Rai|first2=A. N.|last3=Singh|first3=Surendra|date=1988-06-01|title=Effect of cyanophage N-1 development on nitrogen metabolism of cyanobacterium ''Nostoc muscorum''|journal=FEMS Microbiology Letters|volume=51|issue=2–3|pages=145–148|doi=10.1111/j.1574-6968.1988.tb02986.x|issn=0378-1097|doi-access=free}}</ref>

Cyanophages also infect bloom-forming cyanobacteria that can be toxic to health of humans and other animals through the production of microcystin and cause eutrophication, leading to oxygen minimum zones. Cyanophages can infect and kill four common bloom-forming cyanobacteria: ''Lyngbya birgei'', ''Anabaena circinalis'', ''Anabaena flosaquae'', and ''Microcystis aeruginosa'',<ref name=":9"/> and thus may be able to prevent harmful algal blooms under normal conditions. Blooms cause problems ecologically, economically, and in freshwater systems, adversely affect the quality of drinking water.<ref>{{Cite journal|last1=Beversdorf|first1=Lucas J.|last2=Miller|first2=Todd R.|last3=McMahon|first3=Katherine D.|date=2013-02-06|title=The Role of Nitrogen Fixation in Cyanobacterial Bloom Toxicity in a Temperate, Eutrophic Lake|journal=PLOS ONE|volume=8|issue=2|article-number=e56103|doi=10.1371/journal.pone.0056103|issn=1932-6203|pmc=3566065|pmid=23405255|bibcode=2013PLoSO...856103B|doi-access=free}}</ref> Spikes in cyanobacteria populations are usually brought on by nutrient increases due to run-off from fertilizers, dust, and sewage.<ref name=":7">{{Cite journal|last1=Fuhrman|first1=Jed A. |last2=Suttle| first2= Curtis A.|year=1993|title=Viruses in marine planktonic systems |journal=Oceanography |volume=6|issue=2 |pages=51–63 |doi=10.5670/oceanog.1993.14|doi-access=free |bibcode=1993Ocgpy...6b..51F }}</ref>

In addition to regulating population size, cyanophages likely influence phylogenetic composition by allowing other phytoplankton normally inhibited by cyanobacteria to grow.<ref name=":7" /> The specificity with which cyanophages target various hosts also affects community structure. Due to the lysogenic phase of their replication cycle, cyanophages may behave as mobile genetic elements for genetic diversification of their hosts through horizontal gene transfer.<ref>{{Cite journal|last1=Frost|first1=Laura S.|last2=Leplae|first2=Raphael|last3=Summers|first3=Anne O.|last4=Toussaint|first4=Ariane|title=Mobile genetic elements: the agents of open source evolution|journal=Nature Reviews Microbiology|volume=3|issue=9|pages=722–732|doi=10.1038/nrmicro1235|pmid=16138100|year=2005|s2cid=398029}}</ref><ref name=":10" /> Whether the lytic or lysogenic phase dominates in a given area has been hypothesized to depend on eutrophic or oligotrophic conditions, respectively.<ref name=":6" /> Increase in number of encounters is directly related to an increase in rate of infection providing more opportunity for selective pressure, making coastal ''Synechococcus'' more resistant to viral infection than their off-shore counterparts.<ref name=":2" />

==References== {{reflist}}

==Further reading== # {{cite journal |author=Clokie MR, Mann NH |title=Marine cyanophages and light |journal=Environ. Microbiol. |volume=8 |issue=12 |pages=2074–82 |date=Dec 2006 |pmid=17107549 |doi=10.1111/j.1462-2920.2006.01171.x |doi-access=free |bibcode=2006EnvMi...8.2074C }} # {{cite journal |author=Mann NH |title=Phages of the marine cyanobacterial picophytoplankton |journal=FEMS Microbiol. Rev. |volume=27 |issue=1 |pages=17–34 |date=Apr 2003 |pmid=12697340 |doi=10.1016/S0168-6445(03)00016-0|doi-access=free }} # {{cite journal |author=Paul JH, Sullivan MB |title=Marine phage genomics: what have we learned? |journal=Current Opinion in Biotechnology |volume=16 |issue=3 |pages=299–307 |date=Jun 2005 |pmid=15961031 |doi=10.1016/j.copbio.2005.03.007 |bibcode=2005COBt...16..299P }} # {{cite book |last=Suttle |first=CA |editor1-last=Whitton |editor1-first=BA |editor2-last=Potts |editor2-first=M |title=The Ecology of Cyanobacteria: Their Diversity in Time and Space |publisher=Kluwer Academic Publishers |date=2000 |pages=563–589 |chapter=Chapter 20: Cyanophages and their role in the ecology of cyanobacteria |isbn=978-0-7923-4755-2}}

== External links == * [http://www.bluemicrobe.com/bluemicrobeviruses/aboutus.htm the Virus Ecology Group (VEG)] * [https://web.archive.org/web/20130603163753/http://www.phage.org/ the Bacteriophage Ecology Group (BEG)] * [http://www.eebweb.arizona.edu/Faculty/mbsulli/ the Tucson Marine Phage Lab (TMPL)] {{Webarchive|url=https://web.archive.org/web/20150814101748/http://www.eebweb.arizona.edu/Faculty/mbsulli/ |date=2015-08-14 }}

Category:Bacteriophages