Cyanophage
[3] Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins.
[6] 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.
However, the ability of cyanophages to infect multiple hosts and lack of a universal naming system can cause difficulties with their taxonomic classification.
[8] The type species for Cyanomyovirus of the family Myoviridae is Cyanophage AS-1, which was isolated from a waste stabilization pond,[12] and was also the first genus recognized.
[17] Their capsids are polyhedrons that appear hexagonal in 2-D.[14] The tails are hollow with sixfold radial symmetry made of rings of six subunits with unknown orientation.
[15] The host range of cyanophages is very complex and is thought to play an important role in controlling cyanobacterial populations.
[3] They carry short non-contractile tails and cause lysis of several species within three genera of cyanobacteria: Lyngbya, Plectonema and Phormidium.
[18][1][23][24] They play an important role in infecting and causing lysis of members of the genera Nostoc, Anabaena and Plectonema.
[26] To meet the metabolic demand of replication, viruses recruit a multitude of strategies to sequester nutrients from their host.
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.
[27] 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.
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.
[29] Field studies also show that the infection and replication of cyanophages is directly or indirectly synchronized with the light-dark cycle.
[citation needed] Certain cyanophages infect and burst Prochlorococcus, the world's smallest and most abundant primary producers.
[3][37][38] Cyanophage populations have been found to inhabit microbial mats in the Arctic through metagenomic analysis and hypersaline lagoons.
The higher probability of collision may explain why cyanophages of the Myoviridae family primarily infect one of the most abundant cyanobacteria, Synechoccocus.
[3] Evidence of seasonal co-variation between the phages and hosts, in addition to an increase in cyanophages above a threshold of 103 to 104 Synechococcus mL−1, may suggest a “kill-the-winner” dynamic.
[3] Members of the genus Synechococcus contribute ~25% to photosynthetic primary productivity in the ocean, having significant bottom-up effect on higher trophic levels.
[40][41] This is an important step in atmospheric carbon sequestration, commonly referred to as the biological pump, and maintenance of other biogeochemical cycles.
[43][44] 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.
Blooms cause problems ecologically, economically, and in freshwater systems, adversely affect the quality of drinking water.
[45] Spikes in cyanobacteria populations are usually brought on by nutrient increases due to run-off from fertilizers, dust, and sewage.
[citation needed] In addition to regulating population size, cyanophages likely influence phylogenetic composition by allowing other phytoplankton normally inhibited by cyanobacteria to grow.
