Viruses and Algae

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Viruses and Algae

• By Stephanie Boone

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Virus Facts

• Most abundant life form in aquatic systems.
• In the ocean the total number exceeds 1029.
• Marine viruses high concentrations up to 10 8 in
  ml-1
• Play a significant role in the transfer of matter
  and energy in aquatic microbial food webs.
• Infect at least some members of all the major
  classes of freshwater and marine algae.
• Reported in at least 44 taxa of eukaryotic algae
• Includes members 10 of 14 classes of algae
• Virus Interactions range from
• true parasitism (chronic infection/cellular
  release without death)
• to predation (lytic infection resulting in cell
  death).

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Ecological Significance

• Play a significant role in the transfer of matter
  and energy in aquatic microbial food webs.
• Viral lysis of algae effects carbon nutrient
  flow.
• Carbon stored in dissolved organic matter
  released into system.
• May influence carbon cycling and climate.
• Significant role in transfer of information
  through DNA.
• Important role in algae blooms.
• effect marine community structure.

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Algal Viruses

• Despite the established ecological importance of
  marine viruses there have been few studies which
  extensively investigate and characterize viruses
  of algae.
• The viruses studied extensively fall into two
  catagories.

• Large ds DNA viruses.
• PBCV-1, Fsv, EsV
• Small viruses.
• HaRNA, HaNIV

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Large dsDNA Viruses

• Family Phycodnaviridae
• Paramecium bursaria chorella virus (PBCV-1)
  infect eukaryotic unicellular-like green algae.
• Ectocarpus virus (EsV) Feldmannnia virus (FsV)
  infect marine brown alga.
• Common characteristics
• Found on five continents
• tropical, subtropical seawater, and freshwater
• large icosahedral particles 130-190 nm diameter
• large dsDNA genomes 160-380 kb
• Viral capsid assembly and DNA packaging occurs in
  the cytoplasm

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PBVC-1/ Chlorella virus

• PBVC-1 infects chlorella algae strain NC64A or
  Pbi.
• Chlorella algae are small, spherical,
  unicellular, nonmotile, asexual reproducing green
  algae.
• Hereditary endosymbionts in protozoan P.
  bursaria - resistant to viral infection when in
  symbiotic relationship.
• PBCV-1 - linear nonintegrated genome
• 16 classes of virus
• Virus attaches to agal cell wall with hexagonal
  vertices, digests the wall releases viral DNA
  into cell.
• Packaging and assembly of virions takes place in
  cytoplasm virus released by localized cell wall
  lysis

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EsV FsV- Brown algal viruses

• Ectocarpus virus (EsV) and Feldmannia virus (FsV)
  infect brown algae
• densely packed polyhedral viral particles
• do not infect vegetative cells
• viral particles displace normal reproductive
  cells producing sterility
• Viral capsid assembly and DNA packaging occur in
  the cytoplasm after nuclear membrane
  degeneration.

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Small Viruses

• Heterosigma akashiwo nuclear inclusion virus
  (HaNIV) and Heterosigma akashiwo RNA virus
  (HaRNAV) infect the algae Heterosigma akashiwo
  (Raphidophyceae) a toxic bloom-forming microalgae
• Host specific - simultaneous coinfection.
• HaRNAV 25 nm diameter
• polyhedral symmetry
• HaNIV 30 nm diameter
• replicates to high copy number (105) before host
  lysis
• nonenveloped and hexagonal implying icosahedral
  symmetry.
• Each virus forms a crystalline array
• Arrays located in different parts of cell.

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• Conclusion
• Need more research.
• We know very very little about the viruses that
  infect algae.

• References
• Van Etten J L, Meints R H. Giant viruses
  infecting algae. Annual Review of Microbiology
  199953447-494.
• Weinbauer M G, Rassoulzadegan F. Are viruses
  driving microbial diversification and diversity.
  Envirnmental Microbiology 2004 6 1-11.
• Lawrence J E. Chan A M. A novel virus (HaNIV)
  causes lysis of the toxic bloom-forming alga
  Heterosigma akashiwo (Raphidophyceae). Journal of
  Phycology 2001 37216-222.
• Tai V, Lawerence J E, Lang A S, Chan A M, Culley
  A I, Suttle C A. Characetrization of HaRNAV, a
  single stranded RNA virus causing lysis of
  Heterosigma akashiwo (Raphidophyceae). Journal of
  Phycology 2003 39 343-352.