Viruses of Microorganisms

They are highly diverse, with DNA or RNA genomes in various configurations (linear, circular, double-stranded, single-stranded, segmented) and sizes (4.4. to 638 kb).

algal viruses

What do algal viruses infect and lyse?

bloom-forming algae

How do algal viruses direct the evolution of their hosts?

predator-prey selection and genetic exchange

What can algal viruses alter in the environment that is also known as aquatic viral shunt?

composition and distribution of organic matter

This is one of the first algal-virus systems to achieve “model” status.

dsDNA algal viruses infecting Chlorella

This is the best characterized of all the algae-virus models.

Chlorella virus-host model system

Sequencing of the _ genes from Chlorella viruses, Paramecium bursaria chlorella virus 1 (PBCV-1) and NY-2A supported a unique monophyletic viral clade.

DNA polymerase B

Sequencing of the DNA polymerase B (polB) genes from Chlorella viruses, _ and NY-2A supported a unique monophyletic viral clade.

Paramecium bursaria chlorella virus 1 (PBCV-1)

Sequencing of the DNA polymerase B (polB) genes from Chlorella viruses, Paramecium bursaria chlorella virus 1 (PBCV-1) and _ supported a unique monophyletic viral clade.

NY-2A

What family include all of the large dsDNA algal viruses.

Phycodnaviridae

What do you call the group of large dsDNA algal viruses?

Nucleocytoplasmic Large dsDNA Viruses (NCLDV)

What are the hosts of family Phycodnaviridae?

Chlorophyceae, Rhodophyceae & Phaeophyceae

What is the most studied algal virus in family Phycodnaviridae?

Paramecium bursaria Chlorella virus 1

This virus infects Chlorella strains that are endosymbionts of the ciliated protist Paramecium bursaria.

Paramecium bursaria Chlorella virus 1

This family includes the only ssDNA alga-infecting viruses that have been isolated which infect diatoms.

Bacilladnaviridae

Most diatom-virus systems currently in culture are those infecting the genus _.

Chaetoceros

What are examples of dsRNA algal viruses?

MpRV and Chondrus crispus virus (CcV)

This is a dsRNA virus of Micromonas pusilla.

MpRV

This forms its own genus within the family Reoviridae and has been proposed to be the ancestral line of the Reoviridae.

MpRV

This is a dsRNA virus of Chondrus crispus (red seaweed).

Chondrus crispus virus (CcV)

This is a totivirus-like entity that appears to be associated with either a latent or chronic (i.e., particle production below the limit of detection) viral infection that is ubiquitous among red algae.

Chondrus crispus virus (CcV)

What are examples of ssRNA algal viruses?

Heterosigma akashiwo RNA virus, Heterocapsa circularisquama RNA virus 01

This is the only characterized representative of the family Marnaviridae with (+) ssRNA, isometric genome.

Heterosigma akashiwo RNA virus

Their replication appears to be cytolytic, wherein cytopathic effects begin approximately 48 h after infection.

Heterosigma akashiwo RNA virus

This is the only characterized ssRNA virus that infects dinoflagellate; polyhedral (approximately 30 nm in diameter).

Heterocapsa circularisquama RNA virus 01

They are highly species-specific based on host-range experiments.

diatom viruses

These viruses and their hosts represent ecologically important systems that may reveal much on their persistence, co-existence, and competition.

diatom viruses

They do not cause obvious signs of typical virus infection, such as cell lysis or extracellular disease transmission.

mycoviruses

What was the fungi where the first mycovirus was discovered?

Penicillium

They lack an extracellular route for infection.

mycoviruses

They are transmitted intracellularly only through cell division, sporulation, and cell fusion.

mycoviruses

How are mycoviruses transmitted intracellularly?

cell division, sporulation, and cell fusion

They lack a movement protein, which is essential for the life cycle of other viruses.

mycoviruses

Their natural host ranges are limited to individuals within the same or closely related vegetative compatibility groups.

mycoviruses

They are morphologically variable – may be of the bacilliform, rod-shaped.

mycoviruses

Their entire life cycle occurs exclusively within their host cell.

mycoviruses

These viruses replicate within their host but are never released from infected cells to the environment.

mycoviruses

Mycovirus transmission between different strains is restricted by?

fungal vegetative incompatibility

This states that although the origin of mycoviruses is unknown, the association between mycoviruses and fungi is ancient and reflects long-term coevolution.

ancient coevolution hypothesis

This suggests that mycoviruses originated relatively recently from plant viruses; i.e., the original mycovirus was a plant virus that moved from plant to fungus within the same host plant.

plant virus hypothesis

What are the hypotheses about the origin of mycoviruses?

ancient coevolution hypothesis and plant virus hypothesis

They usually remain latent and seldom induce symptoms to their host.

mycovirus

This gained significant attention due to its potential to reduce the crop losses caused by plant-pathogenic fungi.

hypovirulence

They are usually small, with particles less than 70 nm in diameter and genome size of above 7 kbp.

viruses of protozoa

This was described in 2003 and sequenced in 2004 (Megaviridae).

Mimivirus

This was discovered in 2011 (Megaviridae) as the largest virus (440 nm) with the most complex genome (1.2 Mb).

Megavirus chilensis

They infect amoebae and are larger than some bacteria.

Pandoraviruses