Cyanophage

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. Although cyanobacteria metabolize photoautotrophically like eukaryotic plants, they have prokaryotic cell structure. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. 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 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles. 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. Although cyanobacteria metabolize photoautotrophically like eukaryotic plants, they have prokaryotic cell structure. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. 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 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles. The first cyanophage, LPP-1, was discovered in 1963. Cyanophages are classified within the bacteriophage families Myoviridae (e.g. AS-1, N-1), Podoviridae (e.g. LPP-1) and Siphoviridae (e.g. S-1). 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. 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. Many other classification systems used serological, morphological, or physiological properties. 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. Like all other tailed bacteriophages cyanophages have a tail and a protein capsid surrounding genetic material. The double-stranded DNA is approximately 45 kbp long and in some cyanophages encodes photosynthetic genes, an integrase, or genes involved with phosphate metabolism (phosphate-inducible). 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. The type species for Cyanomyovirus of the family Myoviridae is Cyanophage AS-1, which was isolated from a waste stabilization pond, and was also the first genus recognized. The tails have been observed as either contractile or noncontractile with lengths of 20 to 244 nm, widths of 15 to 23 nm, and a shrinking range of 93 nm. Cyanophages generally have isometric hexagonal heads with diameters ranging from 55 to 90 nm. There is large morphological variation in this group, which suggests that they infect a variety of host species. 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. Cyanopodovirus, within the Podoviridae, are present in both fresh and marine water. The type specimen of cyanopodovirus is Cyanophage LPP-1, which infects Lyngbya, Plectonema and Phormidium. Their capsids are polyhedrons that appear hexagonal in 2-D. The tails are hollow with sixfold radial symmetry made of rings of six subunits with unknown orientation. Similar to cyanomyoviruses, they can be found in waste-stabilization ponds and have isometric capsids of similar size but shorter tails. Cyanostylovirus belong to the family Siphoviridae, where the type species is Cyanophage S-1, which is known to infect Synechococcus. Cyanostyloviridae have smaller (50 nm in diameter) isometric capsids than the previous genera but longer tails (140 nm). Other genera in this family have tails that range from 200 to 300 nm in length. The host range of cyanophages is very complex and is thought to play an important role in controlling cyanobacterial populations. 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. The first group is LPP, which belongs to the cyanopodoviruses. This group of viruses includes the original cyanophage isolate that infected 'blue-green algae'. Cyanophages in this group are easy to isolate from the environment. They carry short non-contractile tails and cause lysis of several species within three genera of cyanobacteria: Lyngbya, Plectonema and Phormidium. Thus, the name LPP was derived from the three genera of hosts that they infect. LPP-1 and LPP-2 are two major types of LPP cyanhophages. This group of cyanophages has the same host same range; however, their serum and other body fluids are not the same.