Marine Viruses 4.5 Marine Phages 37
Part A | 4.5
from 4:5 to approximately 6 kb, which can encode
about 11 genes, and most of them have overlapping reading frames [4.11]. Most of the viruses and
morphology are mentioned in Table 4.1. The most
common dsDNA viruses include, Baculoviridae, Herpesviridae, Iridoviridae, Lipothrixviridae, Nimaviridae,
Papovaviridae, Phycodnaviridae, Corticoviridae, Tectiviridae, Myoviridae, Podoviridae, and Siphoviridae.
Baculoviridae, Nimaviridae, and Parvoviridae virus
families are responsible for infection in crustaceans.
Molluscs or mollusks, a large phylum of invertebrates, are the most predominant host for virus families like Herpesviridae, Birnaviridae (dsRNA), Iridoviridae, and Papovaviridae. Iridoviridae is a round,
icosahedral-shaped virus, which can also infect fish.
Herpesviridae, an pleomorphic, icosahedral, and enveloped virus, has a wide range of hosts, including
mollusks, fish, turtles, and mammals. Lipothrixviridae and phycodnaviridae infect archaea and algae,
respectively. The lipothrixvirus is an envelope and
rod shaped, while phycodnavirus is icosahedrallyshaped. Phycodnaviridae is a group of large doublestranded DNA viruses and it can infect important taxa
of marine primary producers including toxic bloom
formers and macroalgae. A marine brown algae infecting phycodnavirus is the Ectocarpus siliculosus
virus (EsV-1), which can encode about 231 proteins
from a 336 kb size of the genome. EsV-1 is a lysogenic virus and the accumulating evidence indicates
that the phycodnaviruses and their genes are ancient [4.12]. RNA viruses are a dynamic, widespread,
and persistent component of the marine virus community. Although a vast number of marine RNA
viruses have not been isolated, the most recognizable marine RNA viruses are positive-sense ssRNA
viruses.
4.5 Marine Phages
Viruses can be arranged in terms of the types of cellular organisms that they infect. Marine phages are
viruses that live as obligate parasitic agents in marine bacteria. The concentration of viruses is approximately 10
7 viruses=mL of surface seawater and the
majority of the viruses are phages. Marine phages
control bacterial abundance and impact the biogeochemical cycle through lysing their host (bacteria).
In addition, marine phages are extremely diverse and
influence their hosts through selection for resistance,
horizontal gene transfer, and manipulation of the bacterial metabolism [4.13]. Sometimes, bacteriophages
are responsible for altering the bacterial genome, gene
expression, and development as emerging bacterial diseases or virulent strain through viral gene transfer.
For instance, a major shrimp pathogen Vibrio harveyi,
converted a nonvirulent strain into a virulent strain
by DNA viruses like Myoviridae and Siphoviridae by
transmission of a toxin gene [4.14]. Corticoviridae, Tectiviridae, Myoviridae, Podoviridae, Siphoviridae, Microviridae, Cystoviridae, and Leviviridae are common
marine phages in the marine environment.
4.5.1 Types of Phage Infection
Phage infections can be categorized into the following types: lytic, lysogenic, chronic, pseudolysogenic,
restricted, and abortive. In lytic infection, the produced
phages release by destroying or lysing the bacterial cells
and only the phage can survive. Lysogeny is a phage
infection in which the phage genome can replicate continually without phage virion formation; in this case
both bacteria and phages survive. The chronic infection effect is similar to lysogeny infection, both bacteria
and phage survive, but it is a productive cycle; the
produced mature phages are released from infected
bacteria by extrusion or budding [4.15]. Some reports
suggest that lysogeny is widespread in marine bacteria, and furthermore, up to 50% of bacterioplankton are
lysogenic [4.16, 17]. The pseudolysogenic stage is a latent or quiescent state; the infecting phage genome does
not replicate and does not produce phage progeny. This
phenomenon is usually induced due to the unfavorable
growth condition for bacteria, and this cycle ends with
either the lytic or the lysogenic cycle, when it turns into
favorable condition. This stage indicates phage and bacteria interactions, which may be crucial for the starving
viral genome in the host and may involve the virulence
of bacteria [4.18]. The bacterium (host) causes death
to the infecting phage via host restriction endonuclease
activity, thus there is no chance for phage progeny replication and production; this type of infection is called
a restricted infection, and only the host only survives
not the phage. Abortive infection involves the death of
both host and infecting phage without production of
phage progeny [4.15].
Part A | 4.5
from 4:5 to approximately 6 kb, which can encode
about 11 genes, and most of them have overlapping reading frames [4.11]. Most of the viruses and
morphology are mentioned in Table 4.1. The most
common dsDNA viruses include, Baculoviridae, Herpesviridae, Iridoviridae, Lipothrixviridae, Nimaviridae,
Papovaviridae, Phycodnaviridae, Corticoviridae, Tectiviridae, Myoviridae, Podoviridae, and Siphoviridae.
Baculoviridae, Nimaviridae, and Parvoviridae virus
families are responsible for infection in crustaceans.
Molluscs or mollusks, a large phylum of invertebrates, are the most predominant host for virus families like Herpesviridae, Birnaviridae (dsRNA), Iridoviridae, and Papovaviridae. Iridoviridae is a round,
icosahedral-shaped virus, which can also infect fish.
Herpesviridae, an pleomorphic, icosahedral, and enveloped virus, has a wide range of hosts, including
mollusks, fish, turtles, and mammals. Lipothrixviridae and phycodnaviridae infect archaea and algae,
respectively. The lipothrixvirus is an envelope and
rod shaped, while phycodnavirus is icosahedrallyshaped. Phycodnaviridae is a group of large doublestranded DNA viruses and it can infect important taxa
of marine primary producers including toxic bloom
formers and macroalgae. A marine brown algae infecting phycodnavirus is the Ectocarpus siliculosus
virus (EsV-1), which can encode about 231 proteins
from a 336 kb size of the genome. EsV-1 is a lysogenic virus and the accumulating evidence indicates
that the phycodnaviruses and their genes are ancient [4.12]. RNA viruses are a dynamic, widespread,
and persistent component of the marine virus community. Although a vast number of marine RNA
viruses have not been isolated, the most recognizable marine RNA viruses are positive-sense ssRNA
viruses.
4.5 Marine Phages
Viruses can be arranged in terms of the types of cellular organisms that they infect. Marine phages are
viruses that live as obligate parasitic agents in marine bacteria. The concentration of viruses is approximately 10
7 viruses=mL of surface seawater and the
majority of the viruses are phages. Marine phages
control bacterial abundance and impact the biogeochemical cycle through lysing their host (bacteria).
In addition, marine phages are extremely diverse and
influence their hosts through selection for resistance,
horizontal gene transfer, and manipulation of the bacterial metabolism [4.13]. Sometimes, bacteriophages
are responsible for altering the bacterial genome, gene
expression, and development as emerging bacterial diseases or virulent strain through viral gene transfer.
For instance, a major shrimp pathogen Vibrio harveyi,
converted a nonvirulent strain into a virulent strain
by DNA viruses like Myoviridae and Siphoviridae by
transmission of a toxin gene [4.14]. Corticoviridae, Tectiviridae, Myoviridae, Podoviridae, Siphoviridae, Microviridae, Cystoviridae, and Leviviridae are common
marine phages in the marine environment.
4.5.1 Types of Phage Infection
Phage infections can be categorized into the following types: lytic, lysogenic, chronic, pseudolysogenic,
restricted, and abortive. In lytic infection, the produced
phages release by destroying or lysing the bacterial cells
and only the phage can survive. Lysogeny is a phage
infection in which the phage genome can replicate continually without phage virion formation; in this case
both bacteria and phages survive. The chronic infection effect is similar to lysogeny infection, both bacteria
and phage survive, but it is a productive cycle; the
produced mature phages are released from infected
bacteria by extrusion or budding [4.15]. Some reports
suggest that lysogeny is widespread in marine bacteria, and furthermore, up to 50% of bacterioplankton are
lysogenic [4.16, 17]. The pseudolysogenic stage is a latent or quiescent state; the infecting phage genome does
not replicate and does not produce phage progeny. This
phenomenon is usually induced due to the unfavorable
growth condition for bacteria, and this cycle ends with
either the lytic or the lysogenic cycle, when it turns into
favorable condition. This stage indicates phage and bacteria interactions, which may be crucial for the starving
viral genome in the host and may involve the virulence
of bacteria [4.18]. The bacterium (host) causes death
to the infecting phage via host restriction endonuclease
activity, thus there is no chance for phage progeny replication and production; this type of infection is called
a restricted infection, and only the host only survives
not the phage. Abortive infection involves the death of
both host and infecting phage without production of
phage progeny [4.15].